鸟类区别于其他各种动物的最显著特征是( )
①体表有羽毛 ②前肢为翼 ③用肺呼吸并用气囊辅助呼吸 ④心脏四腔 ⑤体温恒定 ⑥卵生、体内受精
已知集合A={﹣1,0,1,2},B={﹣2,1,2},则A∩B=( )
从方框中选出下列各旬的最佳应答语。
A.It was good.Thank you.
B.Yes.I could see many stars.
C.I rode a bike yesterday.
D.We went there by plane.
E.I'm 34 kg.
下列事实中,最能说明压力作用效果跟受力面积有关的是( )