摩擦副零件磁粉探伤后，如果退磁不充分，则会（）。
A.加剧磨损
B.加重腐蚀
C.引起冲击
D.摩擦副配合间隙增大
参考答案：A
He used to visit his parents _____, but he is too busy to call on them now.
A every second weeks B every two weeks
C every a few weeks D every two week
描线笔的绘画特点是能帮助使用者达到用线粗细（），特别适合勾勒细小的线条。
A.明晰
B.相同
C.均匀
D.分明
