By the time he realizes he into a trap it’ll be too late for him to do anything about it.

问题补充：

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：

A. walks

B. walked

(答案→)C. has walked

D. had walked

解析：此题考查动词时态。根据句意“截止到他意识到的时候，他已经走进了一个陷阱”以及by常和完成时连用可排除A,B。而且realize用一般现在时的单数第三人称形式，以及后句中用一般将来时，所以选C。