51. What are the largest tributaries of the Missisippi?

The Mississippi River is the chief river of the largest drainage system in North America. With its many tributaries, the Mississippi's watershed drains all or parts of 31 U.S. states and 2 Canadian provinces between the Rocky and Appalachian Mountains. The Mississippi ranks as the fourth longest and tenth largest river in the world. The river either borders or passes through the states of Minnesota, Wisconsin, Iowa, Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana.

52. Why are the Rocky Mountains known as the continental divide?

The Rocky Mountains, commonly known as the Rockies, are a major mountain range in western North America. The Rocky Mountains stretch more than 3,000 miles from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States. Within the North American Cordillera, the Rockies are somewhat distinct from the Pacific Coast Ranges and the Cascade Range and Sierra Nevada which all lie farther to the west .The Continental Divide of the Americas  is the principal, and largely mountainous, hydrological divide of the Americas. The Continental Divide extends from the Bering Strait to the Strait of Magellan, and separates the watersheds that drain into the Pacific Ocean from (1) those river systems that drain into the Atlantic Ocean (including those that drain into the Gulf of Mexico and the Caribbean Sea), and (2) along the northernmost reaches of the Divide, those river systems that drain into the Arctic Ocean.

53. How is wildlife in the us protected?

Saving wildlife is at the core of WWF`s mission. Why? Because animal populations are disappearing at an alarming rate. But even in the face of threats like poaching, habitat loss and overuse of natural resources, WWF is creating a better future for wildlife every day. Protecting these species also contributes to a thriving, healthy planet for people`s health and well-being from forests that slow climate change and filter water to oceans that provide more than one – sixth of the world`s food.We protect wildlife because they inspire us. But we also focus our efforts on those species—like tigers, rhinos, whales and marine turtles—whose protection influences and supports the survival of other species or offers the opportunity to protect whole landscapes or marine areas.

54. Enumerate major national parks where wildlife is protected.

The United States has 59 protected areas,known as national parks, which are operated by the National Park Service, an agency of theDepartment of the Interior. National parks must be established by an act of the United States Congress. The first national park,Yellowstone, was signed into law by President Ulysses S. Grant in 1872, followed by Mackinac National Park in 1875 (decommissioned in 1895), and then Sequoia and Yosemite in 1890. The Organic Act of 1916 created the National Park Service "to conserve the scenery and the natural and historic objects and wildlife therein, and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations."^[1] Many current National Parks had been previously protected asNational Monuments by the President under the Antiquities Act before being upgraded by Congress. Seven national parks (six in Alaska) are paired with a National Preserve. While administered together, they are considered as separate units and their areas are not included in the figures below. The newest national park is Pinnacles National Park, upgraded in 2013.