问题补充：
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：
A. had been
B. is going to be
C. will be
(答案→)D. is
解析：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。
