除医生诊断不适宜乘机者外，怀孕多少周以内的孕妇可按一般旅客乘机，不需经航空公司预先同意。（）
A.32
B.34
C.36
D.38
参考答案：A
当光束通过下列分散系：①有尘埃的空气，②稀硫酸，③蒸馏水，④氢氧化铁胶体，能观察到丁达尔效应的是（ ）
A．①②
B．②③
C．③④
D．①④
We _____ in this pool when we were young, but now it _____ fish.
A．are used to swim; used to keep
B．are used to swimming; used to keep
C．used to swimming; is used to keep
D．used to swim; is used for keeping
