________ fall naturally into two classes, which can be further subdivided into several subclasses.

Not until the Triassic Period ________.

________ planet from the sun, Mars, has a year of 687 days.

The city council is empowered not only to enact new laws, ________ select a new mayor between elections should the need arise.

A giant kind of grass, bamboo may reach a height of 120 feet and ________.

The sea mammal medusa is popularly called a jellyfish because it ________ jelly.

The tallest bird on the North American continent, the white whooping crane, ________ four and a half feet tall.

________ extensively by persons who cannot speak or hear, American Sign Language ranks as the fourth most widely used language in the U.S. today.

In the seventeenth century, North America was vast and unconquered, ________ only at great cost.

By the twenty-first century, the computer ________ a necessity in every home.