Reducing adjective clauses with Perfect Passive

Question

I know we can contract adjective clauses (subject clauses) to phrases. For instance:

1. People who learn English are very smart individuals. / People learning English are very smart individuals.
2. Those two persons who are learning English look awesome / Those two persons learning English look awesome.
3. People who are interested in learning English are incredible ones. / People interested in learning English are incredible ones.

We just leave out the verb subject pronoun + "to be". In most cases.

Nonetheless, my question is connected with the third case when we have Passive Voice. I am wondering, what should I do if I have Present Perfect Passive? The same thing? Omit the auxiliary subject pronoun + "to be"?

4. This work which has been done by my best friend is impressive. / This work done by best friend is impressive.

Although I have never thought about it so deeply, I want to know if I understand it correctly. Passive means that something is performed or done by someone else, especially when the person who makes it is unnecessary for us or simply obvious. In virtue of the examples I found. We can consider action expressed by Passive as that performed by subject?

Answer 1

I'm assuming in your example in (4), you meant to write

"This work done by my best friend is impressive".

In this case, yes, it is understood that the "work done by [your] best friend" is the same as "[your] best friend's work". The sentence makes perfect sense to me as a native American English speaker.

One small thing: In your example in part (3), "ones" sounds strange to me. While I would understand what you mean, it is clear enough without it if you say:

People who are interested in learning English are incredible

or

People interested in learning English are incredible