—How much are these pants?    

—_______ twenty dollars.[ ]

A. It is

B. Its

C. These are

D. They’re

热水系统起解决管道胀缩和水体积膨胀作用的附件为( )。

A．疏水阀
B．补偿器、膨胀罐
C．温度自动调节器
D．减压阀、安全阀、各种闭阀门、水嘴