Gabriel Works as a Waiter for a Catering Business

Gabriel works as a waiter for a catering business. He is scheduled to work an event on Saturday that would earn him $100, Gabriel's sister invites him to go horseback riding on Saturday instead, but Gabriel decides to go to work. This implies that Gabriel's opportunity cost of working is:

A) greater than $100.
B) less than $100.
C) equal to $100.
D) no more than $100.