—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
网友回答
(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。