Official Solution:
The library has not only a large number of books, some of which date back to the 18th century, but also offers a large area for the readers to sit down and read the books.
A. has not only a large number of books, some of which date
B. not only has a large number of books, some of them date
C. not only has a large number of books, some of them dating
D. has not only a large number of books, some dating
E. not only has a large number of books, some of which dating
There are two issues incorporated in the question:
Issue 1. Parallelism: The correlative conjunction
not only A, but also B must use the same parallelism elements A and B.
Issue 2. Subgroup modifier: The three correct forms of a subgroup modifier are as follows: a. Some of which + verb, b. Some of them + participle, c. Some + participle. Other forms of subgroup modifier are wrong.
A. Wrong because of issue 1: not only A, but also B: A = noun phrase (
a large number of books), B = verb (
offers). A noun phrase cannot be parallel with a verb.
B. Wrong because of issue 2: Subgroup modifier form “some of them + verb” is wrong.
C. CORRECT. Issue 1 is correctly addressed. not only A, but also B: A = verb (
has), B = verb (
offers). Issue 2 is also correctly addressed: Subgroup modifier form “some of them + participle” is correct.
D. Same error as in A
E. Wrong because of issue 2: Subgroup modifier form “some of which + participle” is wrong.
Answer: C