An Hour Before Class, You Realize That You Didn't Purchase

An hour before class, you realize that you didn't purchase the textbook for class and there is a quiz. You quickly log on to the book publisher's website, order the e-book, and panic when you realize you've left your wallet in your dorm room. Luckily, you can pay for the book with PayPal. This example illustrates that the publisher's mobile site has done which of the following?

A) simplified payment options for mobile users
B) optimized website design and functionality
C) ensured compatibility with mobile devices
D) gathered marketing insight from customers