连铸坯常见的表面缺陷有鼓肚、扭曲、菱变。
参考答案:错
-May we leave the classroom now?
-No, you _______. You _______ to leave until the bell rings.
A.can't; are allowed
B.mustn't; aren't allowed
C.needn't; are allowed
D.needn't; aren't allowed
P型喷油泵采用()式油量调节机构
A.球销式
B.柱销式
C.拨叉式
D.齿杆式