What part of speech is the italicized word in the sentence below? four score and seven years ago, our forefathers brought forth upon this continent a new nation conceived in liberty and dedicated to the proposition (that) all men are created equal. conjunction adjective adverb pronoun noun

Is the word "that" the italicized word?

quite an interesting way to teach topic sentences, because the answer to this question is the best definition of a topic sentence that one can present, it is as if answering the questions taught you how to do it, this is some real teaching, it is terribly well-done.

the topic sentence in this paragraph is:

topic sentences writers stay on track and keep a paragraph from becoming an aimless collection of sentences about an idea.

which incidentally tells you what a topic sentence should be.