1) Many scientists believe _____ as a result of a collision between the newly formed Earth and a large asteroid.

2) The organ-pipe cactus is _____ in the United States.

3) Willa Cather,_____, gained recognition for her books concerning the American frontier.

4) The average wavelength of visible light is 2,000 times _____ the diameter of an atom.

5) _____ ants live in nests, which may be located in the ground, under a rock, or built above ground and may be made of twigs, sand, or gravel.

6) The tradition of the bowhead whale hunt __back a thousand years and is a vital part of Inuit culture.

7) __the son of an impoverished farmer, was born on Long Island.

8) The primary digestive function of the throat and esophagus is __swallowed materials from the mouth to the stomach.

9) Insulin is manufactured by specialized cells in the pancreas and released __glucose reaches a certain concentration in the bloodstream.

10) One of the basic principles of wildlife conservation involves __adequate natural food and shelter to maintain populations of each species in a given habitat.

11) The decimal numeral system is one of the _____ ways of expressing numbers.

12) Emily Dickinson’s garden was a place _____ great inspiration for her poems.

13) The mountains surrounding Los Angeles effectively shield the city from the hot, dry winds of the Mojave Desert, _____ the circulation of air.

14) Not only _____ to determine the depth of the ocean floor, but it is also used to locate oil.

15) Nebraska has floods in some years, _____.