I will very grateful if you can help me understand the following issue:
As I understand, the next two sentences are interchangeable and have the same meaning:
1) Acts that are done by humans are not necessarily moral.
2) Acts done by humans are not necessarily moral.
The first option is a standard way of using the passive form of the verb. However, I don't understand why the second option is correct, If "done" this case as passive form of the verb or even if it can be treated as an adjective, I am expecting to see some tense of the "be" verb before.
There are many other similar examples, especially when using verbs like: "shown, suggested, presented, defined and etc." with a reference to a previous sentence of our article/text.
Thank you in advance.