---- Did you find your pen this afternoon?
----- No, I didn’t find ________, but I’ve bought _________.
| A．it; it | B．one; one | C．it; one | D．one; it |
You see the lightning _____ it happens, but you hear the thunder later.
| A．the instant | B．for an instant | C．on the instant | D．in an instant |
It is useful to be able to predict the extent _____ a price change willaffect supply and demand.
| A．fromwhich | B．withwhich | C．towhich | D．for which |
I have kept that portrait _____ I can see it every day, as it always reminds me of my university days in London.
| A．which | B．where | C．whether | D．when |
The ability to store knowledge makes computers different from every other machine _____ invented.
| A．ever | B．thus | C．yet | D．as |
_____ quite recently, most mothers in Britain did not take paid work outside the home.
| A．Before | B．Until | C．From | D．Since |