7．Perhaps it will never be known __________ he did with those materials on the incident．
| A．that | B．what | C．which | D．how |
His idea was such a good one ______ we all agreed to use it.
| A．as | B．that | C．so | D．but |
Although the causes of cancer_____, we do not yet have any practical way to prevent it.
| A．are being uncovered | B．have been uncovering |
| C．are uncovering | D．have uncovered |
With just four years _______, the Brazil Olympic organizers have promised to deliver an equally inspirational ceremony.
| A．gone | B．to go | C．going | D．go |
We are so sorry for that．We'll try to determine exactly _________ went wrong that evening．
| A．where | B．what | C．which | D．how |
If you go there by ____train ,you can have quite a comfortable journey ,but make sure you get ___fast one.
| A．/; / | B．/; a | C．the; a | D．the ; / |