Teenagers should ________ to take care of themselves from a young age.
A:educate
B:be educating
C:have educated
D:be educated
给出下列判断:①在数轴上,原点两旁的两个点所表示的数都是互为相反数;②任何正数必定大于它的倒数;③5ab,x2+1,a4都是整式;④x2-xy+y2是按字母y的升幂排列的多项式,其中判断正确的是( )
____