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

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

Comets are still regarded with awe by some people.

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

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

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

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

Some sea urchins海胆 have venomous (toxin) spines

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

People who do not sleep enough tend to become irritable .