C.The value of a motorcycle decrease by 12% each year
D.Every year, the number of online subscribers to a service is 4 times what it was the previous year
Step-by-step explanation:
A function is said to be exponential if it changes (increases or decreases) by a fixed percentage or proportion over a certain period of time.
From the options given, only options C and D is defined as changing based on a certain percentage. And option D cgbages by a clfixed proportion from the initial value.