The professor has received the letter ____ to give a lecture in ftinceton Institute.
| A．being invited | B．to be invited | C．inviting him | D．invited |
There was ______ time _____ Chinese used foreign oil.
| A．a; when | B．a; while | C．/; when | D．/; while |
While ___ along the street, I met an old friend of mine.
| A．I walking | B．was walking | C．I am walking | D．walking |
Your time should be made full use of ________ English well.
| A．learning | B．to learn | C．learn | D．to learning |
Actions __________ walking and drinking are quite difficult in the moon.
| A．for example | B．such as | C．including | D．liking |
Keep ______. The camera is ready.
| A．still | B．calm | C．quiet | D．silent |