The correct answer here is the first choice. A complete sentence must always start with a capital letter. The rest of the words can only be capitalized if those words are proper nouns. Proper nouns like a name of a person, i.e. Jenny, Romeo or Katherine, or it could also be a name of a company or a store like Walmart or Hollister. The rest of the choices (choices two to three) cannot be used since those sentences are considered as one sentence. You can only capitalize when you are starting another sentence.