One-third of the country ______ covered with trees and the majority of the citizens ______ black people.
| A．is; are | B．is; is |
| C．are; are | D．are; is |
When their children lived far away from them，these old people felt ______from the world．（ ）
| A． |
carried away |
B． |
broken down |
| C． |
cut off |
D． |
brought up |
Scientists have advanced many theories about why human beings cry tears，none of ______ has been proved．（ ）
| A． |
whom |
B． |
which |
C． |
what |
D． |
that |
To return to the problem of water pollution，I'd like you to look at a study _______ in Australia in 2012．（ ）
| A． |
having conducted |
B． |
to be conducted |
| C． |
conducting |
D． |
conducted |
Silk ______ one of the primary goods traded along the Silk Road by about 100BC．（ ）
| A． |
had become |
B． |
was becoming |
| C． |
has become |
D． |
is becoming |
We can achieve a lot when we learn to let our differences unite，rather than _______ us．（ ）
| A． |
divide |
B． |
reject |
C． |
control |
D． |
abandon |