Concept:The preposition used after "foreword" is incorrect.
Explanation:The word "foreword" is always followed by the preposition "to", not "of".
This is because a foreword is a short introduction to a book, written by someone other than the author.
It is not a part of the book itself; rather it points toward the book.
Hence, the correct phrase is "foreword to the book".
In the given sentence, part (a) says "after reading foreword of the book".
This is a grammatical error because "of" is inappropriate here.
The other parts (b) and (c) are correct.
Therefore, the error lies only in part (a).
Answer:(a)