Expand or collapse the table of contents using the + or - symbols. Click on a section title to navigate to that section of the article.

Many articles have versions at three different reading levels. Individuals can use the level labels to switch to content most suited to their ability.

Use Page Tools to reduce or enlarge text size, print the full article, generate a citation, translate the article, or create an article excerpt.

Click the play icon to hear the article read aloud.

Double-click any word to see a QuickClick dictionary definition powered by Merriam-Webster. Students can also listen to the pronunciation of the word by clicking on the audio box.