have been是什麼時態怎麼翻譯

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。

What books have been set for the English course?

英語課佈置要用哪些書？