who among the following is a free rider?
a. Ernie listens to National Public Radio, but does not contribute to any fundraising efforts for the National Public Radio.
b. Oscar goes to Elmo’s house to watch a football game on the local television channel.
c. Bert takes the commuter rail to work, but he purchases the discounted monthly passes rather than buying tickets each day.
d. Grover sends his 5 children to a private school rather than to the public school in his neighborhood.