下列关于极限的计算.错误的是( ) A.limn→∞2n2+n+75n2+7=limn→∞2+1n+7n25+7n2=25B.limn→∞=limn→∞2n2+limn→∞4n2+-+limn→∞2nn2=0+0+-+0=0C.limn→∞=limn→∞nn2+n+n=limn→∞11+1n+1=12D.已知an=2-n3-n.则limn→∞=2-11-2-2+3-21-3-2=1924