The correct answer is "ください" because it is the appropriate response to a request or command. In this context, someone is asking for something, and "ください" is the polite way to say "please give it to me" or "please do it". The other options, "りんごです" (It's an apple) and "いらっしゃいませ" (Welcome), do not fit the situation as they do not address the request being made.