environmental damage is done, it takes many years for the ecosystem（生态系统）to recover.
| A．Even if |
| B．If only |
| C．While |
| D．Once |
This vase ________ perfect but for a few small holes in its base.
| A．would have been | B．should have been |
| C．shall be | D．would be |
Tom sacrificed his personal life ________ he could get ahead in his career.
| A．in case | B．as if |
| C．so that | D．only if |
There is still a strong argument ________ mobile phones are a particular risk to children.
| A．when | B．which |
| C．that | D．what |
Students ________ remain in their seats until all the papers have been collected.
| A．shall | B．might |
| C．could | D．will |
John Wood，an Internet blogger，discovered that Samsung ________ for not protecting its workers from a dangerous chemical used on its phones.
| A．had criticized | B．had been criticized |
| C．was criticized | D．was criticizing |