These features were discovered and explored (1) _______ in the late 1940s. The Lomonosov Ridge, the major ridge, cuts the Arctic Basin (2) _______ in half, extending as a submarine bridge 1,800 km (1,100 mi) (3) _______ Siberia to the northwestern tip of Greenland. Parallel (4) _______ it are two shorter ridges: the Alpha Ridge on the North American (5) _______, defining the Canada and Makarov basins, (6) _______ the Arctic Mid-Ocean Ridge on the Eurasian side, (7) _______ the Nansen and Amundsen basins. The average (8) _______ of the Arctic Ocean is only 1,300 m (4,300 ft) (9) _______ the vast shallow expanses on the continental shelves. The deepest (10) _______ in the Arctic Ocean is 5,450 m (17,880 ft).

Two-year postsecondary institutions were first (1) _______ in the United States in the (2) _______ 20th century

Conservation, sustainable use and protection of (1) _______ resources including plants, animals, mineral deposits, soils, clean (2) _______, clean air, and fossil fuels such as coal, petroleum, and natural gas. Natural (3) _______ are grouped into two categories, renewable and nonrenewable. A (4) _______ resource is one that may be replaced over time by natural processes, (5) _______ fish populations or natural vegetation, or is inexhaustible, such as solar energy.

Two-year postsecondary institutions were first (1) _______ in the United States in the (2) _______ 20th century. These schools were called junior colleges (3) _______ their main function was to offer only the beginning (4) _______ of general college study. Credits earned at junior colleges could be transferred to another institution (5) _______ students could complete their final years of college. Now called community colleges, these two-year institutions (6) _______ offer courses of general academic study to recent high school graduates. However, they (7) _______ try to serve the educational needs of a (8) _______ segment of the community, including older students and workers. Today, (9) _______ community colleges offer technical, vocational, preprofessional, and adult-education programs in addition to (10) _______ academic programs

Conservation, sustainable use and protection of (1) _______ resources including plants, animals, mineral deposits, soils, clean (2) _______, clean air, and fossil fuels such as coal, petroleum, and natural gas.

Nonrenewable resources include fossil fuels and mineral deposits, such as (1) _______ ore and gold ore. Conservation activities for nonrenewable resources focus (2) _______ maintaining an adequate supply of these resources well into the future. Natural resources are conserved for their biological, economic, and recreational values, (3) _______ their natural beauty and importance to local cultures. (4) _______, tropical rain forests are protected for their important role in both global ecology and the economic livelihood of the local culture; a coral reef may be (5) _______ for its recreational value for scuba divers; and a scenic river may be protected for its natural beauty.

Approximately one-third of the Arctic (1) _______ is underlain by continental shelf, (2) _______ includes a broad shelf north of Eurasia and the narrower shelves of North America and Greenland. Seaward of the continental shelves (3) _______ the Arctic Basin proper, which is subdivided (4) _______ a set of three parallel ridges and four basins (also (5) _______ as deeps).

These schools were called junior colleges (3) _______ their main function was to offer only the beginning (4) _______ of general college study.