—Tom you look tired this morning. What’s wrong?—I was so busy that I didn’t go to bed 12

问题补充：

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

—I was so busy that I didn’t go to bed 12 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：考查点：连词辨析。解题思路：根据句意：汤姆，今天上午你看起来很累。怎么了？我非常忙以至于昨天晚上12点才上床睡觉。not…until…表示“直到……时候才……”。故选A。