51. I’ll ask her to give you a reply _______she comes back.

A. since

B. before

C. until

D. as soon as

52. ______the headmaster came into the classroom, all the students stop talking to each other.

A. While

B. If

C. Since

D. When

53. Could you tell me______in this popular tourist attraction in winter?

A. if it often snowed

B. whether does it often snow

C. if it often snow

D. whether it often snows

54. Don’t give up regardless of difficulty and failure, ____ you’ll never achieve your goals.

A. and

B. but

C. or

D. so

55. They hurried to the train station, ____ it was too late. They had to wait another ten minutes.

A. but

B. so

C. and

D. or

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