气压焊预热时加热器摆动频率为（）次/min。
A.50～70
B.30～40
C.80～90
D.100～120
参考答案：A
搜索考生文件夹中的FUNC.WRI文件，然后将其设置为“只读”属性。
Mary enjoys living in Beijing, for she has friends there. [ ]
A. a few
B. few
C. a little
D. little
