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The Colorado River carved out a deep canyon in the habitat of an Abert’s squirrel population. This is an example of which stage of speciation?

A. The populations become adapted to different environments and eventually become so different that they cannot interbreed to produce fertile offspring.

B. The populations are isolated and thus do not interbreed.

C. The populations become totally separated from one another.

D. The populations successfully interbreed.

A. The populations become adapted to different environments and eventually become so different that they cannot interbreed to produce fertile offspring.

Explanation:

the national environmental policy act (nepa) is a united states environmental law that promotes the enhancement of the environment and established the president's council on environmental quality (ceq). the law was enacted on january 1, 1970. to date, more than 100 nations around the world have enacted national environmental policies modeled after nepa.