have been to是什么时态?

　　He may have been to some of those places

　　那些地方他也许去过一些。

　　Those who have been to Dalian all say it's beautiful.

　　凡是去过大连的人都说大连很美。

　　I have been to Dalian twice.

　　大连我去过两回。

　　B: I have been to Beijing.

　　B：我去过北京。

　　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。