Scientists say it may be five or six years ______ it is possible to test this medicine on human patients.
| A．before | B．after | C． since | D．when |
Great changes ___ in the recent years.
| A．are taking their place | B．have taken place | C．have been taken place | D．take place |
The reason ___ he didn’t attend the meeting yesterday was ___ his child had fallen ill.
| A．that, why | B．why, that | C．why, why | D．that, that |
The old man ___ us interesting stories when we were young.
| A．were used to tell | B．used to tell | C．got used to tell | D．used to telling |
You should learn from the others ___ you are.
| A．whatever | B．wherever | C．whenever | D．however |
Look! Serveal __ are watching a group of ___ eating grass on the hill.
| A．Germans…. sheep | B．Germans…sheeps | C．German….sheep | D．German…sheeps |