I lived in a home for 13 years, and then converted it to a rental. I moved out to a new home. How do I answer the question "How did you acquire the property?"

You most likely purchased it before you moved in 13 years ago - unless you inherited it or came by it some other way.

Note: Do not use your original purchase price when setting up your rental for depreciation - doing so could cause you a huge headache when you decide to sell.  Please check a reputable home sale site for information on the current market value of your home.