Not having __________ her daughter abroad for a long time, the mother was very worried.
A:heard of
B:heard from
C:learned from
下列对甘地提出的“非暴力不合作运动”的全部内涵,理解最准确的是( )
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( )