非谓语动词里的having done什么时候用呢?
我知道二者有时间区别,可到底怎么区分呢?
－－to reach them on the phone,we sent an email instead.
A.Failed B.Having failed
The country has already sent up three unmanned spacecrafts,the most recent（）at the end of last month.
A.having been launched D.to be launched C.has been launched D.being launched
--that she didn't do a good job,i don't think i am abler than her.
A.To have said B.Having said C.To say D.Saying
Rooftops()with plants,called"gernn roofs",could help fight global warming.
A.covered B.being covered
求详解,