问题
选择题
By the time he realizes he ______ into a trap, it’ll be too late for him to do anything about it.
A．walks
B．walked
C．has walked
D．had walked
答案
答案：C
By the time这里是连词，引导时间状语从句，根据主句的时态是将来时，推断出从句是一般现在时代替一般将来时。