Sam ________ some knowledge of the computer just by watching others working on it.[ ]

A. brought up  

B. looked up

C. picked up  

D. set up

浮球液位开关就是用来控制液体的开关。从形式上主要分为( )。

A．用于污水池内安装

B．用于给水池顶上安装

C．非接触式

D．接触式

E．动荡安装