The magazine is a(n) ______ number. You can take it out of the reading room.
| A．back | B．past | C．old | D．former |
The buses, ____were already full, were surrounded by an angry crowd.
| A．most of them | B．most of which | C．which most | D．that most |
Can you solve such problems ___raised by the audience?
| A．what were | B．as were | C．that were | D．which were |
We often think of the days ___we spent together on the island.
| A．when | B．which | C．in which | D．during which |
Air, _ __we breathe every day, is around us all the time.
| A．that | B．/ | C．which | D．it |
The radio set __ _ last week has been out of order.
| A．I bought | B．I bought it | C．which I bought it | D．what I bought |