This question challenges you to know about the small businesses services that ADP offers its clients, and to fully understand the importance of those offerings. On the ADP website you can see that they offer specific solutions for businesses of all sizes. Show that you are interested in their small business solutions by highlighting a couple of key points.
"I believe that small business benefits from ADP services in many ways. Primarily, your small business services are designed to help a small business owner to proactively manage their company and staff while reducing compliance-related risks that result in costly litigation."