Final answer:
The United States is developing alternative-energy sources due to the scarcity of known petroleum reserves, increasing oil prices, and the dependence on foreign oil.
Explanation:
One reason for the United States to develop alternative-energy sources is the scarcity of known petroleum reserves. The increasing price and volatility of oil prices, along with the dependence on foreign oil, have led to a renewed interest in renewable energy resources to ensure energy security and reduce greenhouse gas emissions. This shift towards alternative sources is driven by concerns related to energy security, carbon emissions, and climate change.
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