Many People Would Like to Sell and Buy on EBay,the

Many people would like to sell and buy on eBay,the most popular of the current Internet auction sites,but they have questions about the process and how to sell and price their merchandise.A company called Keen.com has set up a directory of specialists of whom you can ask questions.When you choose a name and click on the "Call Now" button,the specialist is contacted and will personally call and answer your questions.Keen.com charges a per-minute fee to people who contact its specialist.
-Refer to eBay.Users can see the ratings given to each specialist by previous users before they contact that specialist.Which service component does Keen.com use to help its customers evaluate its service quality?

A) empathy
B) flexibility
C) assurance
D) responsiveness