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

Formulated in 1823, the Monroe Doctrine asserted that the Americas were no longer open to European colonization.

A mythical(imaginary) creature, the dragon was believed to have lion's claws, scaly skin, and fiery breath.

Formerly , in the United States, many nurses worked as private duty nurses rather than in hospitals.

The future survival of the bald eagle is still an important American ecological concern.

Mary McCarthy s satires 讽刺文学 are couched in a prose style that has a classic precision.

In 1974 Henry Aaron broke Babe Ruth's monumental lifetime record of 714 home runs.

Bats fly, rather than glide, and thus are the only mammals capable of true flight.

The company issues an annual report every March.

Some sea urchins海胆 have venomous (toxin) spines

In 1861 it seemed inevitable that the Southern states would break away from the Union.

The first paper was made from the bark of the mulberry tree.

The megaphone(microphone) makes the voice sound louder because it points sound waves in one direction and keeps them from spreading out in all directions.

Blue－green algae grow abundantly in salt marshes.

Ella Grasso, elected governor of Connecticut in 1974, supported the enactment (given, granted) of a freedom-of-information law.

Eyespots, the most rudimentary eyes, are found in protozoan原生动物 flagellates 鞭毛虫 , flatworms 扁形虫 , and segmented worms片段 蠕虫 .

Some cosmetics manufacturers attempt to capture the rose's unmistakable fragrance香味 in soaps and perfumes.

In literature, caricatures讽刺画 usually contain verbal exaggeration through which the writer achieves comic and often satiric 讽刺effects.

The wheels of the first road vehicles were fashioned from crude stone disks.

When carbon is added to iron in the proper proportions , the result is steel.

With the acquisition of smaller companies by larger ones, the 1960's saw a wave of new conglomerates.

While Billie Holiday did not invent the music called "the blues", she most assuredly helped popularize it.

The controls of most modern airplanes can be operated either manually or automatically.

In calculating the daily calorie requirements for an individual, variations in body size, physical activity, and age should be taken into account.

Communication is one of the most important bonds that hold cultural systems together.

Alligators still exist in some of the dank 潮湿 swamps and bayous小海湾 of Alabama's coastal regions.

Urban renewal programs strive to upgrade areas that are becoming slums.

Insect pests are among the leading causes of crop failure.

In the northeastern United States, it rains intermittently 间歇地 throughout the spring.

An oversight 遗漏 (miss, overslaugh) in proofreading often results in printed errors.

The Native American interpreter Sacajawea was a valuable member of the Lewis and dark expedition in 1805.

Cream of tartar 酒石 , a weak acid, can be added to egg whites to help them foam泡沫 when they are beaten

Solid geometry has enabled astronomers to calculate the positions of the heavenly bodies relative to one another.

One of the greatest breakthroughs for professional women came in 1973 when the field of banking opened up for them.

People who do not sleep enough tend to become irritable .

Although the Carbon 14 method of dating old objects is not foolproof , it is the best method available at present

The economy of Dallas, Texas, is strong and diversified .

Comets are still regarded with awe by some people.

The Salk vaccine is a major factor in the fight to eradicate polio.

By the nineteenth century, embroidery on men's clothing had virtually disappeared except for the occasional decorative vest and tie.

Double Eagle in the first transatlantic balloon, was greeted by avid crowds in France.

Some animals pant and sweat to speed evaporation of body moisture and thus cool themselves.

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

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

Food must be moist in order to have a taste.

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

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

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

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?

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