Question

What is teh preposition phrase in tis sentence the world has seen many wars, but the two world wars in the twentieth century have been particularly devastating?

Answer 1

The correct answer should be but the two world wars in the twentieth century

This is a preposition phrase functioning as a subject of a prepositional clause. It's the phrase because it starts with "but" which is used here as a preposition, and is followed by a noun phrase which is "the two world wars in the twentieth century". Phrases don't contain verbs because if they do then they became clauses or are verbal phrases.