How did the agricultural revolution effect later civilizations? give atleast three examples

Which of these statements best describes the ambiguity in this excerpt

Which of the following is an example of one of the successes of the marshall plan? a. a few eastern european countries decided to turn to democracy. b. western european economies were stronger than they had been before wwii. c. borders between western and eastern european countries shifted. d. eastern european countries eventually took part in the plan. ( answer in the format above so i can understand)

When conducting research for forming a hypothesis, which practice should historians follow?