By the middle of the 21st century, the vast majority of the world's population __________ in cities rather than in the country.
| A．are living |
| B．will be living |
| C．have lived |
| D．will have lived |
As middle school students, we _____ the police to keep order.
| A．are used to help | B．used to helping |
| C．used to help | D．used to be helped |
The teacher said he needed _____ boys besides his students _____ the classroom.
| A．20 other; clean | B．20 more; to clean |
| C．20 more; cleaning | D．another 20; clean |
If you keep on, you’ll succeed _______.
| A．in time | B．at one time |
| C．at the same time | D．on time |
We had a hard life _____ in my childhood.
| A．at a time | B．at all times |
| C．at one time | D．at any time |
-----Why does Ling Ling look so unhappy?
-----she has_____ by her classmates.
| A．laughed | B．laughed at |
| C．been laughed | D．been laughed at |