Unlike crested wheatgrass, an alien species from Siberia that forms on

There are two errors tested.
1. Comparison.
2. Parallelism. develop - grow

Unlike crested wheatgrass, an alien species from Siberia that forms only shallow roots and produces tall above-ground shoots, native North American grasses develop an extensive root system, allowing for greater enrichment of the soil, but not grow to be very tall.

A) native North American grasses develop and extensive root system, allowing for greater enrichment of the soil, but not grow to be very tall

B) native North American grasses develop and extensive root system, which allows for their greater enrichment of the soil, but without growing to be that - out due to error - 2

C) the root system of native North American grasses is extensive, allowing for greater enrichment of the soil, but they do not grow to be very out due to error - 1. crested wheatgrass compaired to root system of native North American grass

D) the root system of native North American grasses is more extensive,allowing for the greater enrichment of the soil,but these grasses do not grow to be very - out due to error - 1. crested wheatgrass compaired to root system of native North American grass

E) the extensiveness of the root system of the native North American grasses allows for their greater enrichment of the soil, but they do not grow to be that out due to error - 1. crested wheatgrass compaired to root system of native North American grass
Answer A
By the way the original question may contain a typo. I think it is "an extensive" not "and extensive".

Unlike crested wheatgrass, an alien species from Siberia that forms only shallow roots and produces tall above-ground shoots, native North American grasses develop and extensive root system, allowing for greater enrichment of the soil, but not grow to be very tall.

A) native North American grasses develop and extensive root system, allowing for greater enrichment of the soil, but not grow to be very tall - parallel. "NA grasses develop extensive root system but not grow to be very tall."

B) native North American grasses develop and extensive root system, which allows for their greater enrichment of the soil, but without growing to be that - awkward. "NA grasses develop extensive root system but without growing to be that tall." "growing" is used incorrectly here.

Since crested grass is a variety of grass and we want to compare akin elements we can discard C, D, E. we are left with A and B; even if I don't really like a tree that grows to be very tall, answer B is riddled with errors. Their in B is completely out of place, but without .. that very tall is terrible.

Answer A.
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Unlike crested wheatgrass (X) … native North American grasses (Y) … correct parallelism and comparison. This eliminates C, D, and E.

In A, “allowing for greater enrichment of the soil” modifies the entire clause of “native North American grasses develop an extensive root system” when you have an -ING MODIFIER PRECEDED BY A COMMA, it's an adverbial modifier that modifies the entire preceding clause.

Also, ‘that tall’ is not correct in B. This is acceptable in colloquial English but definitely not in formal written English. This eliminates B.

If you say, John is 6 feet tall but Peter is not ‘that’ tall. In formal English, this sentence is considered incorrect because ‘tall’ is an adjective; to modify an adjective, we need an adverb such as ‘so’ or ‘very’ etc. ‘That’ is not an adverb.

A: Correct

Unlike crested wheatgrass, an alien species from Siberia that forms only shallow roots and produces tall above-ground shoots, native North American grasses develop an extensive root system, allowing for greater enrichment of the soil, but do not grow to be very tall.

(A) native North American grasses develop an extensive root system, allowing for greater enrichment of the soil, but do not grow to be very -- develop and do ot grow are parallel. hence correct

(B) native North American grasses develop an extensive root system, which allows for their greater enrichment of the soil, but without growing to be that --- develop and extensive root system and without growing are unparallel.

(C) the root system of native North American grasses is extensive, allowing for greater enrichment of the soil, but they do not grow to be very -- wrong modification

(D) the root system of native North American grasses is more extensive, allowing for the greater enrichment of the soil, but these grasses do not grow to be very --- wrong modification

(E) the extensiveness of the root system of native North American grasses allows for their greater enrichment of the soil, but they do not grow to be that--- --- wrong modification
_________________

The answer is A
The comparison is correct and it maintains parallelism.
Here but is connecting two verbs and setting up contrast

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Issue 1 - Unlike X, Y - both elements being compared must be equal.
This rule allows us to eliminate C, D and E:
C - Unlike crested wheatgrass, " the root system"
D - Unlike crested wheatgrass, " the root system"
E - Unlike crested wheatgrass, " the extensiveness of the root system"

Unlike crested wheatgrass, an alien species from Siberia that forms only shallow roots and produces tall above-ground shoots, native North American grasses develop an extensive root system, allowing for greater enrichment of the soil, but do not grow to be very tall.

Issue 2 - Parallelism
(A) native North American grasses develop an extensive root system, allowing for greater enrichment of the soil, but do not grow to be very
(B) native North American grasses develop an extensive root system, which allows for their greater enrichment of the soil, but without growing to be that

A - Develop (Verb) an <noun>,....., but do not grow (Verb) to be

B - Develop (Verb) an <noun>,.....,but without growing(noun) to be that (why do we need a relative pronoun here? Redundant) very tall

look at choice B
grasses develop a root system, but without growing to be that tall
the sentence is correct without "but". we do not need "but"
the sentence can contain "but" but it should be
grasses develop a root system with nutrient from the land but without nutrient from the air.
"but" need a contrast.
B is gone

(A) native North American grasses develop an extensive root system, allowing for greater enrichment of the soil, but do not grow to be very - Correct

(B) native North American grasses develop an extensive root system, which allows for their greater enrichment of the soil, but without growing to be that - 'Their' Redundant. Develop an extensive and Without growing - Parallelism.

(C) the root system of native North American grasses is extensive, allowing for greater enrichment of the soil, but they do not grow to be very - Parallelism

(D) the root system of native North American grasses is more extensive, allowing for the greater enrichment of the soil, but these grasses do not grow to be very - Parallelism

(E) the extensiveness of the root system of native North American grasses allows for their greater enrichment of the soil, but they do not grow to be that - Parallelism

KarishmaB - Whenever we have comma+ing modifier, the modifier modifies the clause and is attributable to the subject of the clause. But in this case, however, the modifier "allowing for" doesn't seem to agree with the subject "native North American grasses".

Am I missing anything?

Present participle with a comma at the end of a clause gives cause-effect or 'how'. It modifies either the subject or the entire previous clause. Here it gives us effect of the cause 'develop an extensive root system'.

Check these posts too:
https://anaprep.com/sentence-correction ... rticiples/
https://anaprep.com/sentence-correction ... rticiples/