—Tom you look tired this morning. What’s wrong?—I was so busy that I didn’t go to bed12 o

问题补充：

—Tom, you look tired this morning. What’s wrong?

—I was so busy that I didn’t go to bed12 o’clock last night.

A. until

B. when

C. though

D. unless

答案：

(答案→)A. until

B. when

C. though

D. unless

解析：本题符合not···until的结构，表示直到···才，故选答案为A