eg.
Scientists think that there has been life on Earth for millions of years
科學家認為生命存在於地球已經有幾百萬年了。
have been done現在完成時的被動形式，表示已經被完成
have been doing現在完成進行時，表示到現在為止仍然在進行。
The work has been done.工作已經被完成了。強調結果
They have been playing football for 3 hours.他們已經踢了3小時的足球了。可能還未結束。
強調結果直接用have done現在完成時;
強調過程或還未完成的動作行為用have been doing現在完成進行時。
They have finished the work.
They have been doing the work for a whole day.
I have read the book.
I have been reading the book for a week.
have been
(+-ing動詞)：現在完成進行式
例句與用法:
I have been away from Paris for two weeks.我離開巴黎已經兩星期了。
Flowers soon faded when they have been cut.
花剪下後很快就會枯萎。
Had he not saved me, I might have been drowned.我可能溺死了，若非救了我。
He is said to have been the richest man in Taiwan.
據說他以前是台灣最有錢的人。
She is said to have been an actress about twenty years ago.
據說她在20年以前曾是一位女演員。
