______ I toured Zhangjiajie, I was deeply impressed with its beautiful scenery.
| A．For the first time | B．At first |
| C．It was the first time | D．The first time |
______ made the school proud was ______ more that 90% of the students had been admitted to key universities.
| A．What…because | B．What…that | C．That…what | D．That…because |
There is a new problem involved in the popularity of private cars _______ road conditions need _______.
| A．that; to be improved | B．which; to be improved | C．where; improving | D．when; improving |
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 |
____is certain is ___prevention is more important than treatment .
A．It;that  |
B．What;that | C．As;what | D．What;what |
_______has recently been done to provide more buses for the people ,a shortage of public vehicles remains a serious problem .
| A．That | B．What | C．In spite of what | D．Though what |