______ life began on earth is one of the biggest puzzles that scientist found hard ______.

A. How; solving                 B. When; to be solved

C. How; to solve                    D. Which; to solve

Sir, you ________ take this seat. It’s just for the old.

   A. oughtn’t to     B. can’t          C. won’t          D. needn’t

Can you see that building ______ by trees? That’s ______ we study.

A. surrounded; which                    B. surrounding; where

C. to be surrounded; in which               D. surrounded; where

    I hate ______ when people call me by my nickname (绰号).

A. that         B. one          C. it                   D. 不填

    I hate ______ when people call me by my nickname (绰号).

A. that         B. one          C. it                   D. 不填

_________ wants to enter for the match should reach the given standard.

A. Anyone      B. The one           C. Whoever      D. Who

He said it was this classroom _______ he found his lost watch and _____ he would take good care of it from then on.

A. where; /           B. when; what     C. that; what        D. where; that

________ many changes have _______, we should keep pace with the changes too.

A. Since; taken the place                   B. Because; taken place

C. Now that; taken place                    D. As; been taken place

______ the scene, he couldn’t help thinking of the description in a book ____ by a British novelist.

A. Seeing; written                      B. Seen; written

C. Being seen; writing                  D. Being seeing; written

I believe that those mountains ________ with trees in a few years’ time. 

A. are covered        B. will be covered  C. are covering     D. will cover