John was chosen captain of the team.

Question

in these sentence is captain subject?
Who did this action?John or?What is object in this sentence?
I think that John became captain of the team.Is it right?

Answer 1

Yes, your rephrasing "John became captain of the team" is correct.

John = subject
was chosen = verb (passive voice)
captain = subject complement
of = preposition
the = article
team = object of preposition "of"
[of the team = prepositional phrase modifying "captain"]

In a sentence with a passive verb, the subject does not do the action. Whoever is doing the action is usually indicated by a prepositional phrase beginning with "by" -- such as "by his teammates." This sentence doesn't have that phrase, though, so it is not stated who chose him.