The father often buys his son English learning materials, ____at encouraging him to learn English.
| A．aim | B．aimed | C．to aim | D．aiming |
_______environmental damage is done, it takes many years for the ecosystem to recover.
| A．Even if | B．If only | C．While | D．Once |
In 1941 the US ________ war on the Axis.
| A．informed | B．declared | C．announced | D．related |
The criminal, as well as some ______ people, was arrested by the police yesterday.
| A．sharp | B．relevant | C．vivid | D．skilled |
I was about to go to bed _____ one of my old classmates made a call to me.
| A．when | B．as | C．while | D．that |
Cao Cao’s tomb is reported ________ in China, which attracts nationwide attention.
| A．being found | B．to be found | C．having been found | D．to have been found |