对空气围带应做泄漏试验，试验压力为工作压力的（）倍，检查接头及围带有无泄漏现象
A.1.0
B.1.25
C.1.5
D.1.75
参考答案：B
i为虚数单位，则复数i•（1+i）的虚部为（ ）
A．i
B．-i
C．1
D．-1
You'll have to book a ticket __________ if you want to see that show. [ ]
A. on time
B. in advance
C. on schedule
D. in time
