高速机械在开始工作前应预先进行油循环润滑。
参考答案:对
--Spacecraft "Discovery" has failed in the course of launch.
--_____? They have been preparing for the test.
A.How come?
B.When
C.What for
D.Why not
按住()键,鼠标选择拖动五边形可以复制出一个五边形。
A.Ctrl
B.Shift
C.Alt
D.F1