have been 过去分词是什么时态

His family have been a very positive influence on him.

他的家庭对他有十分良好的`影响。

There have been many changes in recent years.

近几年发生了许多变化。

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

他们一直在努力完善新型号。

None of this would have been possible without their help.

如果没有他们的协助，这事没有一样能办成。

What books have been set for the English course?

英语课布置要用哪些书？