have been made是什么时态

　　Errors may have been made due to human fallibility.

　　这些过失可能是人为犯错造成的。

　　A number of simplifications have been made to the taxation system.

　　税收制度已经历过多次简化。

　　Check that all windows and doors have been made as secure as possible.

　　看看是不是所有的门窗都关紧了。