_____ is certain is ______ the mystery of Stonehenge has never been fully explained.
| A．It, that | B．What, what |
| C．It, what | D．What, that |
—You know. Bob is a little slow ____ understanding, so…
— So I have to be patient ______ him.
| A．in ; with | B．on; with | C．in; to | D．at; for |
We were just about ready to leave _____ it started to snow.
| A．when | B．before |
| C．after | D．since |
_____ the government agrees to give extra money , the theatre will have to close.
| A．Until | B．Unless |
| C．Since | D．While |
It shocked me to see ______ my neighbors treated their children.
| A．why | B．whether |
| C．how | D．since |
Will you deliver, _____ do I have to come to the shop to collect the goods？
| A．and | B．or |
| C．so | D．then |