My mother always wave goodbye to me while I was leaving for school.A. should B. must C. c

问题补充：

My mother always wave goodbye to me while I was leaving for school.

A. should

B. must

C. could

D. would

答案：

A. should

B. must

C. could

(答案→)D. would

解析：考查情态动词。would在句中作“过去常常”之意，故选D。