单项选择（每题1分）
The stones each _____ as much as two tons.
| A．weighs | B．are weighed | C．weigh | D．is weighed |
__________ H7N9 is a deadly virus, it is still safe to eat thoroughly-cooked chicken.
| A．Until | B．While |
| C．If | D．Since |
__________ you may have, you should gather your courage to face the challenge.
| A．However serious a problem |
| B．Whatever serious a problem |
| C．However a serious problem |
| D．No matter how a serious problem |
In China, Some people are quite well-off __________ some live in terrible conditions, especially in remote areas.
| A．though | B．as |
| C．while | D．when |
It's not easy to change habits，__________ with awareness and self-control, it is possible.
| A．for | B．or |
| C．but | D．so |
It is suggested that we __________ watch the movie " Life of Pi"，which will excite us most.
| A．could | B．can |
| C．must | D．should |