Question

identify main clause and subirdinate clause 1 .. what is done cannot be undone​

Answer 1

Main clauses have a subject and verb and can stand on their own. Subordinate clauses begin with a conjunction and therefore cannot stand on their own.

So “What is done” is a noun phrase serving as the subject of the sentence. You might be able to argue that “What is done” is a subordinate clause because it does indeed have both a subject and a verb — but a clause also is supposed to express a complete thought, and “What is done” does not express a complete thought.

“Can be undone” is the verb. You could also argue that “can be” is the verb, and “undone” is a predicate adjective.

With “What is done” reduced to the position of a noun phrase, you only have one clause in the sentence.