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 discovered

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 discovered

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 discovered

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 discovered

 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 discovered

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 discovered

 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 discovered

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

1. A.
   discovered
2. B.
   have discovered
3. C.
   had been discovered
4. D.
   have been discovered

 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 discovered