You are building a chatbot for a travel agent. The bot will ask users for a destination and must repeat the question until a valid input is received, or the use...

You are building a chatbot for a travel agent. The bot will ask users for a destination and must repeat the question until a valid input is received, or the user closes the conversation.
Which type of dialog should you use?

A. prompt B. input C. adaptive D. QnA Maker