The controls of most modern airplanes can be operated either manually or automatically.
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When carbon is added to iron in the proper proportions , the result is steel.
The economy of Dallas, Texas, is strong and diversified .
Alligatorsstillexistinsomeofthedank潮湿swampsandbayous小海湾ofAlabama'scoastalregions.
The first important exposition in the United States was held in Philadelphia in 1876.
All living organisms, regardless of their unique identity, have certain biological, chemical, and physical characteristics in common.