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【单选题】
曲柄摇杆机构中低副的个数是A.
4
B.
5
C.
6
D.
7
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反馈参考答案：
举一反三
【单选题】They ______ on the program for almost one week before I joined them, and now we _____on it as no good results have come out so far.
A.
had been working; are still working
B.
had worked; were still working
C.
have been working; have worked
D.
have worked; are still working
【简答题】They _______ on the program for almost one week before I joined them,and now we _______ it as no good results have come out so far. A．had been working; are still working B．had worked; were still wor...
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