工件内孔在粗镗后有圆柱度误差，则在半精镗后会产生（）。
A.圆度误差
B.尺寸误差
C.圆柱度误差
D.位置误差
参考答案：C
若x=123456789×123456786，y=123456788×123456787，则x，y的大小关系是（ ）
A．x=y
B．x＜y
C．x＞y
D．不确定
The students _______ busily when Miss Brown went to get a book she _______ in the office.
A．had written, left
B．were writing, has left
C．had written, had left
D．were writing, had left
