Barnes & Noble spun off the NOOK, its unprofitable e$-$reader. Shoppers couldn't get beyond identifying Barnes & Noble as a destination for books; however, most people are not buying hard copies of books and instead are using e$-$readers. The NOOK, though an e$-$reader, has different features from the Amazon's Kindle. The Kindle is inexpensive, easy to use, and syncs up easily with an Amazon digital account. This example shows that product failure results from all of the following EXCEPT

a$.$ overestimation of market size

b$.$ incorrect positioning

c$.$ a low price

d$.$ an inferior product