—Jack ________ride a motorcycle to work.

— Yes, but now he ________ there as motorcycles are not allowed on our city streets.

A．used to; is used to walk

B．was used to; is used to walking

C．was used to; is used to walk

D．used to; is used to walking

数控机床的进给量一般根据（）进行选取。

A.零件材料硬度

B.零件加工余量

C.零件加工精度

D.零件加工表面粗糙度

E.刀具构料

F.工件材料