Approximately, how many national parks are there in the united states?
a. 25
b. 50
c. 120
d. 474

The correct answer is b. 50
The United States has 59 known national parks or protected area that are operated by National Park Service under the agency of Department of the Interior. Examples of National Park in US are Yellowstone, Acadia, American Samoa, Canyonlands, Death Valley, Glacier, Gran Canyon, Redwood, Sequoia, Yosemite and others.

Answer the use of flood plains and irrigation;