I believe the answer is: Reference group
Reference group refers to the group that become subjects of comparison to another group of individual.
Most people use this reference group to measure our own worth (for example, if you want to know whether you a bad or good guitar player, the reference group that you would most likely use would be famous band member) , and this might influence the formation of our identity in the future.
B. Sails
The Egyptians were among the first to use sails on their ships to improve transportation.
I'm guessing It could do both but I'm going more with hurting
It shows that the president gets to check in on the other branches and see if they are doing something they shouldn'. It shows that the president has a say in the other branches and other branches have a say to his.
Cave men are humans but went extinct in Europe 40,000 years ago. There are many myths about this and I am pretty sure there is not a correct answer yet. Great question though!