The controls of most modern airplanes can be operated either manually or automatically.
A、bythebookD
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The Salk vaccine is a major factor in the fight to eradicate polio.
Bythenineteenthcentury,embroideryonmen'sclothinghadvirtuallydisappearedexceptfortheoccasionaldecorativevestandtie.
Solidgeometryhasenabledastronomerstocalculatethepositionsoftheheavenlybodiesrelativetooneanother.
With lasers scientists can probe many physical processes, such as combustion, once beyond our ken.视野
ThefuturesurvivalofthebaldeagleisstillanimportantAmericanecologicalconcern.
