I have finished a large part of the book ; the rest _____more difficult.

A.is　B.are  C.was  D.were

I have finished a large part of the book ; the rest _____more difficult.
  A.is　　　　　 B.are　　　　　 C.was　　　　　　　　　 D.were

I have finished a large part of the book ; the rest _____more difficult.

A.is　　　　　 B.are　　　　　 C.was　　　　　　　　　 D.were

I have finished a large part of the book ; the rest _____more difficult.

A. were　　　　　 B. are　　　　　 C. was　　　　　　　　　 D. is

I have finished a large part of the book, the rest of which___ more difficult.