This computer doesn’t work properly, because the operating system has .
| A．broken up | B．broken down |
| C．broken out | D．broken away |
Don’t litter in the street in Singapore, you could be arrested.
| A．or | B．and | C．but | D．so |
In the past several weeks, many cities in Northern China from heavy fogs and severe cold.
| A．had suffered | B．have been suffering | C．were suffered | D．suffered |
she was out of the room, he took a quick look at the papers on her desk.
| A．If | B．While | C．Though | D．Unless |
Visitors to the hills are greeted by signs them to look out.
| A．warn | B．to warn | C．warning | D．warned |
It is already well understood causes the global warming.
| A．what | B．when | C．that | D．how |