毛知母顶端有残留的毛状浅黄色叶痕及茎痕，称为（）
A.金钱眼
B.金钱环
C.金井玉栏
D.金包头
E.果黄
参考答案：D
若a，b∈R，已知直线x+a2y+1=0与（a2+1）x-2by+3=0互相垂直，则|ab|的最小值为______．
— Why can’t the boy understand what the American teacher said?
— Because he is a beginner, _______ he knows ________English.
A．and; a little
B．and; little
C．so; little
D．so; a little
