It was along the Mississipp
i River Mark Twain spent much of his childhood.
| A．how | B．which | C．that | D．where |
_______environmental damage is done, it takes many years for the ecosystem to recover．
| A．Even if | B．If only | C．While | D．Once |
．Every possible means _______to prevent the air pollution, but the sky is still not clear．
| A．are being used | B．have been used |
| C．has been used | D．had been used |
．______ surprised the family most was ________the girl played basketball very well．
| A．That; that | B．That; what | C．What; that | D．What; what |
．I have to see the doctor because I________a lot lately．
| A．cough | B．coughed |
| C．have been coughing | D．had coughed |
．The cost of renting a house in central Baoji is higher than________in any other area of the city．[来
| A．one | B．it | C．this | D．that |