Scientific interest in providing suitable habitats for bottom-dwelling

Meaning analysis:

Scientific interest in (something) :
(something) = providing suitable habitats
habitats for who: for bottom-dwelling animals (such as river clams arises)
- not because they are important sources of human food
- but from their role as an integral link in the Aquatic food chain.

so overall the sentence s conveying that scientist are interested in providing habitats to bottom dwelling animals. And they (scientists) wants to do that for 2 reasons, 1. because they (animals) are important food resource and 2. because they are also playing important role in aquatic food chain

Error Analysis:
Observe the stem after underline portion, "but from their role as an integral link in the Aquatic food chain". this tells , parallelism issue and not as x but from y

(A) not because they are important sources of human food - out
(B) although they are not an important sources of human food - absurd
(C) not in that they are important as human sources of food - abusrd
(D) not from their importance as a source of human food - ok
(E) not from being important sources of food for human beings - use of "being" and idiom, not from x but from y

co relative conjunction error type
not from their ...... but from their ; ll structure and word meaning sentence stays logical
IMO D:

Parallelism is being tested here.
The idiomatic structure here is not correct. The right answer is d

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OFFICIAL EXPLANATION

The error in this sentence is one of lack of symmetry in structure in a ‘two-part’, sentence. The given sentence seeks to contrast between two reasons why there is scientific interest in providing suitable habitats for bottom-dwelling animals. In idiomatic English, these two reasons must be stated in the same grammatical form. The second reason (which is nonunderlined) is mentioned as ‘but from their role as an integral link’. ‘To have perfect balance with this construction, the first part must be of the form ‘not from their’ followed by a noun phrase. (A) does not have this form, and is not the answer.

(B) and (C) can also be easily eliminated for the same reason.

Both (D) and (E) start with ‘not from’, but it is (D) which has these two words followed by a noun phrase ‘their importance as a source of food’. So, (D) is the answer.

(E) unnecessarily uses a gerund, and is also followed by a plural noun ‘sources’ thereby disturbing symmetry with the nonunderlined part.