FLEX10第6步指的是（）。
A.升温
B.冷却
C.消毒
D.阀开
参考答案：C
When you read the book, you'd better make a mark ____ you have any questions. [ ]
A. at which
B. at where
C. the place
D. where
燃气表安装时距出厂日期最多不应超过（）月。
A、12
B、9
C、6
D、3
