TheSalkvaccineisamajorfactorinthefighttoeradicatepolio.
Blue-green algae grow abundantly in salt marshes.
Alligatorsstillexistinsomeofthedank潮湿swampsandbayous小海湾ofAlabama'scoastalregions.
The first important exposition in the United States was held in Philadelphia in 1876.
Communicationisoneofthemostimportantbondsthatholdculturalsystemstogether.
Comets are still regarded with awe by some people.