I think its D.... because it started in China.
The civil war allowed the world to see how unnecessary slavery was and pushed for the 13th amendment to abolish slavery and give blacks equality because it was tearing the country apart.
I believe the answer is: Equalizer.
Parking brake adjustment is commonly done by reducing the length of the cables to remove unnecessary slack.
Tightening the nut on the equalizer would pretty much do the job and reduce the excessive slack.
Answer:
This is true, opportunity cost does mean how much you have to spend to do something