have been made是什么時(shí)態(tài)

　　Errors may have been made due to human fallibility.

　　這些過失可能是人為犯錯(cuò)造成的。

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

　　稅收制度已經(jīng)歷過多次簡(jiǎn)化。

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

　　看看是不是所有的門窗都關(guān)緊了。