证书有有效期吗?
参考答案:
有,一般为3年。
Sarah pretended to be cheerful, _____ nothing about the argument.[ ]
A. says
B. said
C. to say
D. saying
He works as an engineer now, but he _____ on a farm for three years.
A.has worked
B.worked
C.was working
D.had worked