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 banking systems of the world have many similarities, _____ they also differ, sometimes in quite material respects.
7.
Learning that takes place in infancy provides the____ for the eventual transformation of a child into an adult.
8.
In the late 1930's and early 1940's, Jacob Lawrence created many paintings _____ the lives of famous African American activists.
9.
The Centennial Exposition, _____ in Philadelphia, Pennsylvania, in 1876, celebrated the one-hundredth anniversary of the Declaration of Independence.
10.
In the dark abyss of the deep sea _____ is produced by luminescent fish.
11.
The classic American novel Moby Dick____ an account of the conflict between human beings and their fate.
12.
In the metals industry, hydrogen is used to prevent metals from tarnishing while undergoing_____.
