He failed the final examination and only then ____ how much time he had wasted.
| A．he realized | B．had he realized |
| C．he had realized | D．did he realize |
Today’s teens don’t see anything strange in the fact _______the computer takes up a central place in their social lives.
| A．which | B．that | C．where | D．what |
I _______to go shopping that Saturday, but the bad weather made me change my mind.
| A．plan | B．would plan | C．had planned | D．have planned |
---______ the farmers discovered the entrance to the secret cave in the valley?
--- Totally by chance.
| A．When was it that | B．How was it that | C．How it was that | D．When it was that |
One more month, _______ the grapes in the yard will be ripe.
| A．or | B．otherwise | C．but | D．and |
_______these coins are of different shapes, sizes and colors, they all date back to a long, long time ago.
| A．Since | B．Unless | C．Once | D．While |