【题目】Only when Lily walked into the office ______ that she had left the contract at home.
A.she realized
B.has she realized
C.she has realized
D.did she realize

【答案】D
【解析】句意：只有当莉莉走进办公室的时候，她才意识到她把合同忘家里了。本题考查only位于句首，引导的时间状语从句，主句要主谓倒装。根据时态和句意可知选D。