Two people came to look at the house, but ________ wanted to buy it. [      ]

A. none of them

B. neither of them

C. none of whom

D. neither of whom

半数有效量是指( )。

A．临床有效量的一半

B．LD₅₀

C．引起50%动物产生反应的剂量

D．效应强度

E．以上都不是