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 the guide dog, the blind man found the way go home.

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 the new equipment, our factory produced ________ VCD players in 2001 as the year before.

A. as many as twice      B. twice more than       C. as twice many   D. twice as many