---Where are my family photos, Jim?

---I don’t know. Maybe_______ on the dresser.

A．these are

B．those are

C．they are

D．this is

采取（）的方法可以起到防止水击的作用。

A、缩短阀门的关闭时间

B、增加管内流速

C、在管道上设置空气罐

D、在泵出口加止回阀