Answer:
The correct option is:
The hotel doorman for opening the door for him
Explanation:
A gratuity( also called as a tip) is a sum of money that is given by a client or customer to a service worker in addition to the basic price.
It is given to certain service sector workers for a service performed.
Tips and their amount are a matter of social custom and etiquette, and the custom may vary between countries and settings.
So, Adam should offer a tip to:
the hotel doorman for opening the door for him.