---How long____?
---Sine 2000.
A.had the machine been used
B.has the machine been used
C.will the machine be used
D.was the machine used
参考答案:b
since就说明还没结束,所以不用a
更不是将来时和过去时,所以不用c,d
---Sine 2000.
A.had the machine been used
B.has the machine been used
C.will the machine be used
D.was the machine used
参考答案:b
since就说明还没结束,所以不用a
更不是将来时和过去时,所以不用c,d