The number of private cars in urban areas should be limited ___________the number of public buses should be increased.
| A．when | B．while | C．unless | D．until |
The bell rang and came in Mr.Brown, a book in his hand. Then the class began.
| A．for | B．when | C．with | D．while |
In the past 5 years a great deal of money _____ improving the environment of the school.
| A．is spent | B．has been spent | C．was spent | D．had been spent |
China has been working very hard to stop the endangered animals ______ .
| A．dying out | B．dying away | C．dying down | D．dying hard |
I ______their method of making the machine .
| A．adopted | B． voted | C． elected | D． commanded |
The blues has been _____part of African-American culture since then, and it is still ______ important part of American culture.
| A．a; a | B．/ ; an | C．the ; a | D．/ ; a |