3.3 课时作业
Ⅰ.用括号内所给动词的适当形式填空
1．With the help of high technology, more and more new substances ________ (discover) in the past 50 years.
2．The construction of the new bridge ________ (complete) by now.
3．She ________ (laugh) at by her classmates since she was young.
4．Every possible means ________ (try) to save the wild animals up to now.
5．How many suggestions ________ (give) to you so far?
6．The plans ________ (study) by the experts for four times.
7．This is the second time that he ________ (praise) by his teachers this week.
8．Much of its traditional folk culture ________ (keep) alive ever since it was born.
9．A lot ________ (do) in the recovery of national economy in the past few years.
10．Students are told to make sure that the windows ________ (close) before leaving the classroom.
答案：1.have been discovered 2.has been completed
3．has been laughed 4.has been tried
5．have been given 6.have been studied
7．has been praised 8.has been kept
9．has been done 10.have been closed
