A:y=50(1﹣x)2
B:y=50(1﹣2x)
C:y=50﹣x2
D:y=50(1+x)2
亚洲所在的半球为( )①南半球 ②北半球 ③东半球 ④西半球
下列哪一组是鸟类所特有的特征?( )
①体表有羽毛; ②用肺呼吸并用气囊辅助呼吸; ③体温恒定
④体内受精; ⑤有发达的神经系统; ⑥前肢变成翼
Many airlines now allow passengers to print their boarding passes online ______ their valuable time.