如果物体绕一点作旋转式的动作，那么这种动作就是旋转现象。[ ]
正确
--- How wide is the river?
--- About ________.
A．100-metres-wide
B．100 meters wide
C．100-metre-wide
D．100 meter wide
Usually pilots need about a decade of experience _______ they can be promoted to captain.
A．after
B．before
C．then
D．when
