Which, if any, is the best way to improve these sentences from the passage?

answer; ///i believe that the correct answer is (a) the great depression

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."

a. poison gas was sprayed over battlefields by airplanes to weaken enemy positions before major attacks.