Scientific interest in providing suitable habitats 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.
(A) not because they are important sources of human food
(B) although they are not an important source of human food
(C) not in that they are important as human sources of food
(D) not from their importance as a source of human food
(E) not from being important sources of food for human beings
The error in this question is one of lack of symmetry 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 noted in the same grammatical form. The second reason which is non-underlined is mentioned as ‘but from their role as an integral link’.
To have perfect construction 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, so is not the answer.
(B) and (C) must also be 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’ there by disturbing symmetry with the non-underlined portion.
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