—Does your sister work as a teacher in Canada? —No but she once there for five yearsA. t

问题补充：

—Does your sister work as a teacher in Canada?

—No, but she once there for five years．

A. taught

B. had taught

C. has taught

D. would teach

答案：

(答案→)A. taught

B. had taught

C. has taught

D. would teach

解析：had taught表示过去的过去，这里没有可以参照的过去的动作，故排除B；has taught现在完成与现在有关，故排除C；would teach过去将来时，过去说将要做的事，不符合语境，故排除C；taught过去式跟现在没有关系，是持续性动词，可与时间段连用，故选A。