车床主轴（）使车出的工件出现圆度误差
A.径向跳动
B.轴向窜动
C.摆动
D.窜动
参考答案：A
—Look! Here comes our school bus.
—No hurry. Don't get on it ______ it has stopped. [ ]
A. until
B. after
C. since
D. when
