People who do not sleep enough tend to become irritable .

The first important exposition in the United States was held in Philadelphia in 1876.

Despite the proliferation of other faster modes of transportation, the railroads remain the largest carriers of intercity freight in the United States.

How many people are aware that a dancer with the New York City Ballet typically wears out a minimum of two hundred pairs of toe shoes per year?

The fear of smallpox, which terrorized the eighteenth century, has no analogy(likeness) today.

All living organisms, regardless of their unique identity, have certain biological, chemical, and physical characteristics in common.

The flower bud of a water lily 百合 opens at sunset since .its opening is triggered(commence) .by the decreased light.

Food must be moist in order to have a taste.

With lasers scientists can probe many physical processes, such as combustion, once beyond our ken.视野

Some children display an unquenchable 难以抑制的 curiosity about every new thing they encounter.