Formulatedin1823,theMonroeDoctrineassertedthattheAmericaswerenolongeropentoEuropeancolonization.
A、emphaticallystatedThe Salk vaccine is a major factor in the fight to eradicate polio.
TheNativeAmericaninterpreterSacajaweawasavaluablememberoftheLewisanddarkexpeditionin1805.
Some children display an unquenchable 难以抑制的 curiosity about every new thing they encounter.
Insect pests are among the leading causes of crop failure.
Bats fly, rather than glide, and thus are the only mammals capable of true flight.
