舵的类型按舵叶的支承情况分有（）
①双支承舵；
②多支承舵；
③悬挂舵；
④半悬挂舵。
A.①②对
B.①②③对
C.①②③④对
D.③④对
参考答案：C
在煤质分析中，除特别要求外，每项分析试验应对同一煤样进行两次测定，一般称为重复测定或平行测定。
He told me that by the end of this year they______together for twenty years．
A．would work
B．had been working
C．will have worked
D．would have been working
