By the time he retires, professor Baker _____ for almost forty years．
A.will have taughtB.had taughtC.has taughtD.is teaching在线课程A
解析：
试题
分析：句意：到贝克讲授退休时，他将从事教育40年了。这里教授还未退休，退休发生在将来，又因为By the time故用将来时的完成时，故选A。考点：考查将来完成时的用法。
点评：本题难度适中。将来完成时是高中阶段动词的时态类比较难以理解的一种时态。考生往往与一般将来时混淆，一般将来时指从现在来看将要发生的动作；
而将来完成时指在将来某个时间之前已经完成的动作。即学即练：Had you joined the chat room ten minutes ago, you would have known what we _{___a}bout then.A. had talkedB. have talked C. talk D. were talking解析：D。句意：如果你十分钟前加入聊天室，你就会知道（那时）我们在谈什么。