I would say vapor pressure, but I could be wrong. Good luck ^^
I am pretty sure the answer is D. That the patterns of a polarity matched up on both sides.
Answer: I believe it is artificial selection (not certain though)
Explanation: modern day dogs have been bread an domesticated to be used by humans in ways we see fit.
If they need 4 people to a pulley then they would need a 8 to two pulleys
here is the equation
4people*2/pulley*2
8people/2pulley