Immigrants often stayed in neighborhoods with other people from the same country. What were these neighborhoods called?

Ethnic Enclaves

Explanation: Throughout history, we see immigrants moving from one place to the other and  often staying in neighborhoods with people with whom they shared the same nationality, culture and similar habits.

a social contract.

"a social contract is an agreement between citizens and their leader where the citizens give up certain freedoms in exchange for protection. the constitution of the united states is an example of a social contract."

b.

one company controls all the means of production of a product.

~coco