Correct option is C
A. All plastics are fruits.
B. All fruits are books.
C. No books are trousers.

I. Some books are plastics (True)
Since all plastics are fruits and all fruits are books, it follows that some books are plastics.
II. No trouser is a plastic (True)
From Statement C, No books are trousers, and since all plastics are books, it follows that no plastics are trousers.
III. Some fruits are plastics (True)
Since all plastics are fruits, it follows that some fruits are plastics.
IV. Some trousers are fruits (False)
No books are trousers, and since all fruits are books, it follows that no fruits can be trousers.
Thus, the Correct option is (c) Only conclusions I, II, and III follow.