单项选择题
There have been（）medicine in the last 50 years.
A.great advancesin B.a great advancein C.great advanceon D.a great advanceon
单项选择题 Would you mind（）us how old you are?
单项选择题 50% of the people（）for the survey were female.
单项选择题 There are many cities（）very fast.
