Naddition to replacing the president if necessary, it's the duty of the vice president to a. serve as liaison to the judicial branch. b. review laws before the president signs them. c. serve as speaker of the house. d. preside over the senate.

explanation:

the addition to geographic boundaries that might have  kept the people of the huang river civilization from traveling to far distance region is that they had learned about the other river valley civilizations but feared contact would bring invasion.

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