气相色谱法测定氯苯类化合物时，若水样中氯苯含量较高，萃取后可以不浓缩直接上机测定。
参考答案：对
I don’t know if he ____ us; if he ____, I’ll let you know.
A．will come and help; comes
B．comes and helps; will come
C．will come and help; will come
D．comes and helps; comes
--- How are you feeling here?
--- It’s quite hot. I don’t know _____ to go or stay.
A．how
B．when
C．whether
D．where
