physician assistant studies.
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.
an employee's increased output after additional training
mark brainliest : )