-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