—Mum,  can I go skating now?

—Well,  you may go after your homework _____. [ ]

A. has finished

B. will finish

C. is finished

D. was finished

根据磁感应强度的定义式，下列说法中正确的是（   ）

A．在磁场中某确定位置，B与F成正比，与I、L的乘积成反比

B．一小段通电直导线在空间某处所受磁场力F=0，那么该处的B一定为零

C．一小段通电直导线放在B为零的位置，那么它受到磁场力F也一定为零

D．磁场中某处的B的方向跟电流在该处所受磁场力F的方向相同