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.