One evening when it was so warm I stayed awake until half past eleven in order to have a

问题补充：

One evening when it was so warm, I stayed awake until half past eleven in order to have a good look at the moon by myself.

A. on average

B. on purpose

C. on sale

D. on schedule

答案：

A. on average

(答案→)B. on purpose

C. on sale

D. on schedule

解析：句意，一天傍晚，天气很暖和，直到十一点半我都没有睡觉，为了亲自看一下月亮。on average平均起来on purpose故意地on sale有售on schedule按时间表，根据题意，故选B。