have加been加過去分詞是什么時態

　　There have been some problems but basically it's a good system.

　　雖然出現過一些問題，但這基本上仍不失為一個好系統。

　　His family have been a very positive influence on him.

　　他的家庭對他有十分良好的影響。

　　There have been many changes in recent years.

　　近幾年發生了許多變化。

　　They have been working on the perfection of the new model.

　　他們一直在努力完善新型號。

　　None of this would have been possible without their help.

　　如果沒有他們的協助，這事沒有一樣能辦成。