Question

By the time he retires, professor Baker _____ for almost forty years．

A．will have taught	B．had taught
C．has taught	D．is teaching

Answer 1

：A

：考查时态。By与完成时连用，by后面的时间状语从句用一般现在时代替将来时，所以主句中用将来完成时。句意：等到他退休的时候，Baker教授将已经教了40年的书了。故A正确。