Plastic bags are provided for our convenience but they have also_______ the pollution of the environment．
| A．adapted to | B．turned to | C．contributed to | D．looked forwarded to |
I will accept Guy coming with us, ________ he pays for his own meals.
| A．only if | B．so that |
| C．ever since | D．even though |
Scientists are warning that ________ emissions of carbon (碳排放) are cut, we could be heading for an environmental disaster.
| A．before | B．as |
| C．unless | D．in case |
——Did you inform Helen of the plan put forward at the meeting?
—Of course. ________ I saw her.
| A．So long as | B．If only |
| C．The moment | D．Any time |
Please call my secretary to arrange a meeting this afternoon, or ________ it is convenient to you.
| A．whenever | B．however |
| C．whichever | D．wherever |
She usually keeps her valuables, such as jewels and money, ________ she believes secure.
| A．even if | B．in case |
| C．where | D．that |