buy的過去式和過去分詞是？

例句：

The curtains were an impulse buy.

這窗簾是一時心血來潮買下的.。

We need to buy some new furniture.

我們需要買一些新傢俱。

Now is a good time to buy a house.

現在買房子正是時候。

They only buy the best.

他們只買最好的。

Try the shoes on before you buy them.

鞋子要先穿上試一試再買。

It may be necessary to buy a new one.

也許有必要買個新的了。