问题补充:
Mrs. White became a teacher in 1985. She for twenty years by next summer.
A. will teach
B. would have taught
C. has been teaching
D. will have been teaching
答案:
A. will teach
B. would have taught
C. has been teaching
(答案→)D. will have been teaching
解析:语境中的时间信息:by next summer 到明年夏天,提示该题应为将来时,故排除B、C。根据句意:怀特夫人自1985年成为教师,到明年夏天就将教书法家了。因此,只有将来完成进行时才能表示这个将来某时前一直进行的动作。故选择D。