The Key to the Success of E-Books Has Been ______

Multiple Choice

The key to the success of e-books has been ______.

A) the creation of an e-reader that has a comfortable-to-read display
B) the creation of an e-reader that was affordable for a large audience
C) having a large number of titles available electronically
D) making e-books less expensive than hardcover copies
E) All of the options are correct.