The Moon. The Moon completes an orbit around Earth in about 27.3 days.

Earthquake. The magnitude of earthquakes is measured by the Richter scale.

Flood. In 1993, the Great Midwest Flood killed 48 people and caused $18 billion in damage.

England. A CAT scan is a series of x-rays that are assembled by a computer to create detailed images.

Northeast. Estuaries are a transition zone between river environments and ocean environments.

Erythrocyte. Erythrocytes are responsible for delivering oxygen to body tissues.