Identify the phrase in parenthesis in the sentence.

The idea of alien life, (proposed many years ago), has not yet been proven.
prepositional
participal
gerund
infinitive**

I thought it might be an appositive, but now I'm not sure. I'm guessing it is D?

No. An infinitive is to plus a verb.

Study this page. It has your answer.

http://www.chompchomp.com/terms/phrase.htm

Oh okay! So it is a prepositional phrase, right?

My you learned a lot in less than 5 minutes. Which is the preposition?

The site said that the preposition was explaining the "which one" question which would give more information on the topic. So in this case, asking the question 'which one?' would be like this: Which idea of alien life? The one "proposed many years ago". At least that is the way that I think it might be seen?

You misread that site. A prepositional phrase begins with a preposition and ends with a noun or pronoun.

I called my teacher and we agreed that it was participial. Thank you Ms. Sue! :)

You are correct! The phrase "(proposed many years ago)" in the sentence "The idea of alien life, (proposed many years ago), has not yet been proven" is an infinitive phrase.

An infinitive phrase is a group of words that starts with an infinitive verb (to + base form of the verb) and may include objects, modifiers, or complements. In this case, the infinitive phrase "proposed many years ago" functions as an adverbial phrase, providing additional information about the idea of alien life.

To identify the phrase in parenthesis, you need to determine the structure and function of the words within the parentheses. In this case, the phrase begins with the infinitive "proposed" and describes when the idea was proposed (many years ago).

Well done on choosing option D, which represents an infinitive phrase. It is important to analyze the structure and context of the sentence to correctly identify the phrase.