_____ human beings live in great numbers, the waters are very likely to become contaminated.
| A．That | B．Where | C．Even if | D．Though |
Suddenly a good idea occurred to her, but she couldn’t find any paper ______.
| A．to write | B．to write on |
| C．written | D．writing on |
Thailand has decided to begin building its first standard-gauge railways in cooperation with China, ______may cost $12.2 billion.
| A．when | B．that | C．it | D．which |
— Excuse me, can you show me the way to the nearest bus stop?
— Sorry. I’m a stranger here. I ______ here until my guide arrives.
| A．stand | B．have stood |
| C．am standing | D．will stand |
When Mary arrived she found all her children ______ for nearly two hours.
| A．have gone to sleep | B．fell asleep |
| C．was falling asleep | D．had been asleep |
The silence of the library ______only by the sound of pages being turned over.
| A．had been broken | B．breaks |
| C．broke | D．was broken |