Question

Which homophone best completes the sentence? ________ not going to believe what I just heard about the principal

Answer 1

Which homophone best completes the sentence?

You're not going to believe what I just heard about the principal.

A homophone is two or more words that share the same sound but their meanings, origin, and sometimes spelling are different.

The homophone in the sentence would be "you're" which sounds exactly like "your" but both differ in meaning. "You're" is a contraction of "you are", whereas "your" is a possesive noun indicating belonging.  

Answer 2

You're, because it is a homphone (you're, your) and makes sense in this sentence.