在室内给水系统中，可起到加压和稳压作用的设备包括（）。

A．水泵

B．高位水箱

C．贮水池

D．气压罐

For an investment portfolio, the Sharpe ratio is best described as a(n): （）

A. Relative measure that indicates risk per unit of mean return. 

B. Absolute measure that indicates risk per unit of mean return. 

C. Relative measure that indicates mean excess return per unit of risk.