A:He can give his seat to them.
B:He can read newspapers to them.
C:He can help them carry bags.
19÷3____7 13÷2____13÷3
39÷9____8 24÷5____24÷4
下列示意图能够反映古代印度种姓制度的是( )
下列动物中不属于环节动物的是( )
氢原子从能级m跃迁到能级n时辐射红光的频率为υ1,从能级n跃迁到能级k时吸收紫光的频率为υ2,已知普朗克常量为h,若氢原子从能级k跃迁到能级m,则( )