I have finished a large part of the book ,the rest of which ()more difficult . 为什么/答案是 is为什么?谢谢1

Question

I have finished a large part of the book ,the rest of which ()more difficult . 为什么/
答案是 is
为什么?谢谢1

Answer 1

I have finished a large part of the book ,the rest of which (is)more difficult .
the rest of which 中which 指前面the book 即the rest of the book 意思是剩下的部分（比较难）.这里把剩下的部分做一整体,就用单数来表示.