单选题 For the sake of efficiency, you are supposed to turn in your proposal ______ next Monday morning at the latest.

(A) on
(B) until
(C) for
(D) by

【正确答案】 D

【答案解析】[理由] by+明确时间+at the latest 最迟不超过……
[例] You should finish the work by two o'clock at the latest
=You should finish the work no later than two o'clock.
(你最迟应当在两点以前完成工作。)
根据上述，(D)应为正选。