the problem of land erosion getting more serious, the local government is searching for a way to deal with it.
| A．As | B．With | C．When | D．If |
John knocked at the door for nearly five minutes____his wife opened it.
| A．when | B．before | C．until | D．as |
---The thread of my kite broke and it flew away.
---I told you it would easily break_____was the weakest.
| A．where | B．the place where | C．for it | D．where it |
They were surprised that a child could work out the problem____they themselves couldn't.
| A．once | B．while | C．then | D．if |
.I had been puzzled over the problem for over an hour without any result, _____ all at once thesolution flashed across my mind.
| A．while | B．when | C．then | D．as |
Sally worked late in the evening to finish her report _____ her boss could read it first thing next morning.
| A．because | B．so that | C．before | D．or else |