问题

With the help of high technology, more and more substances _________ in the past years

A:discovered
B:have discovered
C:had been discovered
D:have been discovered

正确答案是：

同类题型

Police have asked witnesses of the accident to ___________, as the victim is critically wounded, unable to give an account of the accident.

The passengers were ________in the traffic congestion which resulted from the accident ahead.

Christmas is a holiday usually celebrated on Dec25 ________ the birth of Jesus Christ

The parcel _____ so much that I dropped it on the stair.

.It was a cold winter night,and there wasn’t anyone _________ the boy could turn to for help in the street.