It is pretty well understood __________controls the flow of carbon dioxide in and out the atmosphere today.
| A．that | B．when | C．what | D．how |
The little boy won't go to sleep __________ his mother tells him a story.
| A．or |
| B．unless |
| C．but |
| D．whether |
I don't believe we've met before，__________ I must say you do look familiar.
| A．therefore |
| B．although |
| C．since |
| D．unless |
It was a nice meal，__________ a little expensive.
| A．though |
| B．whether |
| C．as |
| D．since |
__________ all of them are strong candidates, only one will be chosen for the post.
| A．Since |
| B．While |
| C．If |
| D．As |
You will be successful in the interview __________ you have confidence.
| A．before |
| B．once |
| C．until |
| D．though |