Reverse auctions are bidding or tendering systems in which the buyer places an item for bid on a request for quote system; then potential suppliers bid on the job, with the price reducing sequentially, and the lowest bid win

petroleum engineering.

nurse anesthesia.

physician assistant studies.

mathematics.

political science.

marketing.

healthcare administration.

computer science.

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   : )