When it______ air pollution, Beijing faces the three “C” s-----cars，coal and construction，which lead to Beijing's thick air pollution.
| A．refers to | B．comes to | C．happens to | D．speaks to |
Small cars are ___ of fuel, so they have more appeal for consumers.
| A．free | B．short | C．typical | D．economical |
Put the ___ of your tongue against your upper teeth when you produce the sound.
| A．tip | B．top | C．peak | D．pole |
China has promised to revise its existing regulations and ___ new policies according to WTO requirements.
| A．forming | B．to form | C．to be forming | D．have formed |
In the dream Peter saw himself ___ by a fierce wolf, and he woke suddenly with a start.
| A．chased | B．to be chased | C．be chased | D．having been chased |
___ the employees' working efficiency, the supervisor will allow them to have a coffee break.
| A．Improving | B．To improve | C．Having improved | D．Improved |