A 2015 study by the U.S. Department of Energy found that currents

The actual sentence -
A 2015 study by the U.S. Department of Energy found that currents in U.S. waters were capable of generating up to 2000 terawatt-hours of energy each year, enough to meet half the country’s energy demand.

i.e.

Currents were capable of generating up to 2000 terawatt-hours of energy each year, enough to meet half the country’s energy demand.

What is enough to meet half the country’s energy demand?
- Up to 2000 terawatt-hours of energy each year.
Thus, the phrase "enough to meet half the country’s energy demand" is a noun modifier that modifies the energy or precisely "up to 2000 terawatt-hours of energy each year"
This construction has no issue.

A) enough to meet half the country’s energy demand.
Looks correct. Hold on.
B) which was enough to meet half the country’s energy demand.
"which" wrongly modifies "year"
C) and this was enough to meet half the country’s energy demand.
What is the antecedent of "this" ? Can't be -up to 2000 terawatt-hours of energy each year.
"This" is a demonstrative pronoun and can't stand alone to refer any noun.
D) and was enough to meet half the country’s energy demand.
S-V mismatch.The subject is plural "currents in U.S. waters ". Can't use was here.
E) meeting half the country’s energy demand.
Currents were capable of generating ...., meeting half the country’s energy demand.
Note: The participle modifier at the end (after comma) modifies the entire preceding clause and applies to the subject.
It can -
1. reflect the outcome of the action.
2.the way the action is performed.
In this case, there is no action.
Note that the sentence says "Currents were capable of generating" and not that "Currents were generating".
Thus, the participle modifier after comma is not correct here.

IMO A

A 2015 study by the U.S. Department of Energy found that currents in U.S. waters were capable of generating up to 2000 terawatt-hours of energy each year, enough to meet half the country’s energy demand.

A) enough to meet half the country’s energy demand. Correct

B) which was enough to meet half the country’s energy demand. Incorrect

which modifies energy that changes meaning

C) and this was enough to meet half the country’s energy demand. Incorrect

antecedent of this is not clear

D) and was enough to meet half the country’s energy demand. Incorrect

currents ...were ....and was........... - currents plural, was singular

E) meeting half the country’s energy demand. Incorrect

it changes meaning, before underlined portion there is no action that is continuous

A sounds better

If we select option A, is it not a run on sentence?

Or it is acting as adverbial modifier.

Can anybody explain. Thanks!

Run-on sentence comprises of two sentences without adequate punctuation or conjunctions.
A sentence must have subject and verb.
There is no other sentence here.
"enough to meet half the country’s energy demand" is not a sentence, but just a modifier.

I agree with that but then how does "enough to meet half the country’s energy demand" modify energy?

The sentence hold the structure:

X does Y, <a phrase>

The phrase can modify :
1.entire preceding clause with -How aspect of action OR Result of the action
(remember the cases of comma + participle modifier and absolute modifiers)
2.the nearest noun/noun phrase (if Y is a noun or noun phrase).

Let's see if it meets case 1.
In this case, "enough to meet half the country’s energy demand" can't modify entire sentence.
Ask yourself - what is enough? If you try to modify entire clause, you will end up believing that - Currents were capable and outcome of "this capability" resulted in enough something. But currents (the subject) did not do anything here.
Now, in case 2
"up to 2000 terawatt-hours of energy each year" is a noun phrase (with the main noun "energy")
Thus, 2nd case fits the bill.

Hope it helps.

A 2015 study by the U.S. Department of Energy found that currents in U.S. waters were capable of generating up to 2000 terawatt-hours of energy each year, enough to meet half the country’s energy demand.

A) enough to meet half the country’s energy demand. -- The phrase correctly modifies '2000 terawatt-hours of energy'.

B) which was enough to meet half the country’s energy demand. -- usage of which incorrectly modifies the noun right next to the comma 'year'.

C) and this was enough to meet half the country’s energy demand. -- usage of this creates a pronoun antecedent error.

D) and was enough to meet half the country’s energy demand. -- was refers to currents in U.S. waters and this creates a SVA error.

E) meeting half the country’s energy demand. -- 'meeting' implies it's already happening, however, the currents 'were' able to - past tense.

Answer should be Option A.

[quote="generis"]


A 2015 study by the U.S. Department of Energy found that currents in U.S. waters were capable of generating up to 2000 terawatt-hours of energy each year, enough to meet half the country’s energy demand.

A) enough to meet half the country’s energy demand.

B) which was enough to meet half the country’s energy demand.

C) and this was enough to meet half the country’s energy demand.

D) and was enough to meet half the country’s energy demand.

IMO A

A) enough to meet half the country’s energy demand. --CORRECT

B) which was enough to meet half the country’s energy demand.-- Which refers to year .Wrong

C) and this was enough to meet half the country’s energy demand. -- this refers to what?? was is not the right verb for currents

D) and was enough to meet half the country’s energy demand. -- Same verb error as C

E) meeting half the country’s energy demand. -- Use of Verb-ing modifier is wrong here

A 2015 study by the U.S. Department of Energy found that currents in U.S. waters were capable of generating up to 2000 terawatt-hours of energy each year, enough to meet half the country’s energy demand.

A) enough to meet half the country’s energy demand. -> this phrase is modifying the previous sentence. It makes sense. Let's keep it.

B) which was enough to meet half the country’s energy demand. -> which is modifying "each year" It is not the intended meaning of the argument. Incorrect.

C) and this was enough to meet half the country’s energy demand. -> and indicates parallelism, but "this was" and "that currents" are not parallel. Incorrect.

D) and was enough to meet half the country’s energy demand. -> Same as C. Incorrect.

E) meeting half the country’s energy demand. -> "enough to meet" in A is better than "meeting..." Incorrect

So, I think A.

Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.