Solid geometry has enabled astronomers to calculate the positions of the heavenly bodies relative to one another.
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Urban renewal programs strive to upgrade areas that are becoming slums.
Communication is one of the most important bonds that hold cultural systems together.
The megaphone(microphone) makes the voice sound louder because it points sound waves in one direction and keeps them from spreading out in all directions.
TheNativeAmericaninterpreterSacajaweawasavaluablememberoftheLewisanddarkexpeditionin1805.
The controls of most modern airplanes can be operated either manually or automatically.