问题
选择题
Allen has decided that he will be an engineer by the time he ________ twenty.
A．had been
B．is going to be
C．will be
D．is
答案
答案：D
答案：D 考查考生对题干和动词时态的理解及掌握情况。句中by the time相当于when，用来引出时间状语从句，从句中需用一般现在时表将来，故选D。