Answer:i think it is a and b because
so do encorage to rebel against each other
Explanation:
The First Transcontinental Railroad was a 1,912-mile continuous railroad line constructed between 1863 and 1869 that connected the existing eastern U.S. rail network at Omaha, Nebraska/Council Bluffs, Iowa with the Pacific coast at the Oakland Long Wharf on San Francisco Bay.
The Great Wall is a fortificated East-to-West line which historically has delimited the Chinese Northern border. Its primary purpouse was to defend the Chinese territory against the invasions and quick raids organized by the nomadic people from the Eurasian Steppe lands, located more to the North.
But rather than as a fixed border, it should be regarded as a transition zone which establishes a distinction between two different lifestyles, even nowadays: the farmer regions in the South with sedentary ways of life and the pasture lands in the North, where its inhabitants have nomadic lifestyles and work mainly in animal husbandry activities.
