国际照明委员会1931年规定的色光三原色是（）.
A、黑、灰、白
B、青、品红、黄
C、红、绿、蓝
D、蓝、品红、黄
参考答案：C
常用的浸提方法包括( )
A．法 B．水蒸气蒸馏法 C
B．超滤法
C．盐析法
----- As we know, you won’t go back to the USA since you have established a research center here．But how long _____ in America?
----- For almost 10 years．
A．did you study
B．have you studied
C．were you studying
D．have you been studying
