Which sentence is capitalized correctly?

“What a beautiful sunset we had last night!” I said.

“what a beautiful sunset we had last night!” I said.

“What a Beautiful Sunset we had last night!” I said.

“What a beautiful sunset we had last night!” i said.

The sentence capitalized correctly is: "What a beautiful sunset we had last night!" I said.

The sentence that is capitalized correctly is: "What a beautiful sunset we had last night!" I said.