Only when he arrived home that he had left his key in the office.A. will he realizeB. he

问题补充：

Only when he arrived home that he had left his key in the office.

A. will he realize

B. he did realize

C. did he realize

D. should he realize

答案：

A. will he realize

B. he did realize

(答案→)C. did he realize

D. should he realize

解析：only+状语主句采用部分倒装，本题叙述的是过去的事情所以应该用一般过去时态答案为D。