a is not usually thought of as an economic activity, although it could lead to one. good contacts are never to be dismissed. i'd say a is not the answer.
b with decorations. no money or services have exchanged hands. b is not the answer.
d picking up a relative at the airport. generally d is not the answer. we don't charge our relatives for services given (although if it kept them away, maybe that wouldn't be such a bad thing).
c the key word is selling. money for products. this is true economics. here's your answer.
service orientation is the ability and desire to anticipate, recognize and meet others' needs, sometimes even before those needs are articulated