To make low-profit customers more profitable the abc bike shop-
a) sends birthday greetings to its best customers and gives them discounts on merchandise.
b) has a club for its regular customers, organizing cycling events and parties for them.
c) allows existing customers to upgrade to a newer model by trading in their older model.
d) though it previously offered free delivery, now charges for deliveries made outside the city.
e) encourages customers to send in their suggestions for product improvement.