What is a sentence using the word unbelievable?
i have an unbeilivable dog, it bounces.
"It's unbelievable" is a sentence. It contains a subject (It) and a predicate (is unbelievable). In this case, the subject (It) and verb (is) are put together in the form of a contraction (It's). That is just fine. When you wrote it, you forgot the apostrophe in the contraction. Just add in the apostropheand capitalize the I for it's, and your sentence is fine. It's unbelievable.