Mary’s skirt looked just the same as Joan’s, but it cost __________ hers.

A．as much twice as

B．twice as much as

C．much as twice as

D．as twice much as

关于磁场，下列说法正确的是 （　　）

A．磁感应强度大的地方，通电导线在磁场中该处受到的磁场作用力也大

B．磁感线越密的地方磁感应强度越大

C．通电导线在某处所受磁场力为零，则该处的磁感应强度为零

D．磁场的方向就是通电导线在磁场中某处受到的磁场作用力的方向