为保证样品检测时仪器处于最佳工作状态，PMT校准采用（）
A.样品
B.质控品
C.鞘液
D.生理盐水
E.缓冲液
参考答案：B
Just as the saying goes, “_______”, computer games also have some disadvantages though they are popular among teenagers.
A．No garden is without weeds
B．Every little makes a nickel
C．Time waits for no man
D．The onlooker sees the game best
在现况研究中，通过调查通常可以获得（）
A.发病率
B.患病率
C.罹患率
D.死亡率
E.病死率
