3km以上单线隧道应采用的出碴方式是（）。
A.有轨运输
B.无轨运输
C.斜井运输
D.竖井运输
参考答案：A
两位数乘一位数，积可能是______位数，也可能是______位数．
--------Why didn't Nick come to school yesterday?
--------_______ he was ill.
A．After
B．Where
C．When
D．Because
