Answer: E. Having enough books to satisfy customer demands versus the cost of having the inventory
Explanation: It is always a primary challenge in any sales business, how to balance customer needs, i.e whether there will be enough goods / books for customer needs, and the cost of purchasing the inventory. The point of any sale is profit, so if the supply of inventory is large and the sale is weak, it is certainly not good for the sales business, and therefore the challenge of how to predict the sale, i.e how much to purchase the inventory. Book sellers can always expect some customers to buy a book, though they can never predict whether a book will become a best seller, even if it is written by a politician or celebrity, this can never be foreseen, so the challenge of purchasing supplies is all the greater. It sounds tempting to sell a politician's book, so it may seem like a criterion for getting a large amount of supplies, but whether it's going to sell well, it's that balance that really needs to be anticipated, and it's a challenge.