Gamebox, a seller of video-gaming systems, games and online gaming subscriptions, recently made available a coupon that allows its gaming subscription members to extend their subscriptions by three months at no charge. Subscribers need only to login to the website using their user name and password and provide the coupon code. Because this contract modification (from 12 months to 15 months) does not add distinct goods or services from the original contract, Gamebox need only make a cumulative catch-up adjustment.
a) true
b) false

Since in the question it is mentioned that the members who takes subscription could extend their subscriptions without paying any kind of an additional charges. here they can do by signing in and used their coupon code also it does not involved different goods or services so the Gamebox required only adjustments

Therefore the given statement is true as it involved the adjustments and the same is to be considered