Final answer:
The National Environmental Policy Act of 1969 was the first legislative act to mandate environmental impact studies for federal projects.
Explanation:
The first legislative act that required government agencies to conduct studies on the environmental impacts of federal projects was the National Environmental Policy Act of 1969 (NEPA).
This act laid the foundation for environmental protection and paved the way for subsequent laws like the Clean Water Act of 1972 and the Clean Air Act of 1970.
NEPA aimed to ensure that the environmental consequences of federal actions were considered and addressed in decision-making processes.
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