单项选择题
All students （） a loud laugh when professor Henry Mitchel told them the joke.
A. let off B. let down C. let out D. let up
单项选择题 I prefer the climate in Kunming to（）in Wuhan.
单项选择题 If you（）see Mr. Jim, you give him my regards.
单项选择题 There is less crime now than there used to be. It seems that there is a （） in the crime rate.
