Choose the best answer from the 4 choices .

Choose the best answer from the 4 choices .
Choose the best answer from the 4 choices .
1.Since the introduction of the new technique,the production cost ____ greatly.
A.reduces B.is reduced C.is reducing D.has been reduced
2.I hope they ____ this road by the time we come back next summer.
A .have repaired B.will repair C.are to repair D.will have repaired
3.Three new buildings ____ on the campus by the end of this year.
A.will be built B.are going to be built C.will have been built D.have been built
4.By the time you get there tomorrow,they ____ for Beijing.
A.will have left B.are leaving C.will leave D.are to leave
5.It was not until I ____ your telephone that I knew the truth.
A.got B.had got C.have got D.will get
6.Even though Ella ____ English for three years before she came to the U.S.A.it is still difficult for her to make her understand.
A.studied B.had studied C.has studied D.has been studying