真题练习

539.With the help of high technology,more and more new substances _____ in the past years.

A.discovered
B.have discovered
C.had been discovered
D.have been dicovered

540.I have got a headache.
No wonder.You _______ in front of that computer too long.

A.work
B.are working
C.have been working
D.worked

答案解析

539.答案是D;in/during the past years与现在完成时连用，new substances应该被发现，故用被动形式。
540.答案是C;此处表示过去开始的动作对现在的影响及结果。