被动语态一个超短但是很难的汉译英句子，帮帮忙噢。。

These cookies have been finished.

你应该说明一下你的中文句子想表达什么意思
饼干吃完了 还是怎么了

吃完了直接可以have been finished.

如果用finished cookies 都已经没了 怎么还these are...？

做完的饼干：
I have finished cooking these biscuits.
There're some finished biscuits.

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你问过去分词作adj.
如：
A finished job. 完成的工作
Finished goods 成品

就是过去分词可以修饰后面的名词 也表一种被动

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补充你的问题：

These are the cookies that/which have been finished”
这个也可以 用了定语从句
但是现在英语写出来越简洁越好 直接将finished作为分词就可以了

一般我们用定语从句都是将2个句子拼在一起 缩短句长
如：
He will lend several books which/that he bought yesterday to me.
这里我们看出来是2个句子 一个是他借我书 另一个：他昨天买的

而有的却没有必要：
The cloths designed by Tom is popular now.
这里就省略了The cloths which/that is designed by Tom...

these are finished cookies

这种不叫被动语气,是过去分词用于形容词

these cookies are finished by jack (这些