have been to是什么时态

　　Staff have been retrained to use the new technology.

　　为使员工学会运用新技术，对他们进行了再培训。

　　Several computer engineers have been contracted to the finance department.

　　有几位计算机工程师与财务部门签订了合同。

　　I must have been insane to agree to the idea.

　　我肯定是犯傻了，居然同意了这个想法。

　　Six theatre companies have been selected to take part in this year's festival.

　　已选定六个剧团参加今年的`戏剧节。

　　A number of people have been employed to deal with the backlog of work.

　　已雇来一些人处理积压的工作。