小明在玩磁铁时，磁铁掉进沙子里，拿出来什么也不沾；若磁铁掉进铁屑里，拿出来时，磁铁两端上沾满了铁屑，这一现象说明了：①______；②______．如果磁铁不小心掉到硬地面上摔断了，则折断处两边是______磁极．（选填“同名”或“异名”）

---Could you tell me _____?

---About two months.

A．when are you leaving for Shanghai

B．how often you go to the school library

C．how many tickets have you booked

D．how long you have been at this school