气缸套外表面出现蜂窝状孔群的故障叫（）.
A.拉缸
B.穴蚀
C.穿孔
D.抱缸
参考答案：B
Jack was sure to get this year’s scholarship as the standards of scholarship were not terribly_________
A．tough
B．rough
C．difficult
D．demanding
什么叫厚度自动控制系统（AGC）？
