热洗清蜡方式操作简单、清蜡效果明显，有效防止了（）对捞油井捞油的影响。
A、水
B、气
C、结垢
D、结蜡
参考答案：D
for the free tickets,I would not have gone to the film so often.
A．If it is not
B．Were it not
C．Had it not been
D．If they were not
已知展开式中，各项系数的和为64，则n等于（）．
A．7
B．6
C．5
D．4
展开式中，各项系数的和为64，则n等于（）．