（1+3x）n（其中n∈N且n≥6）的展开式中x5与x6的系数相等，则n= [ ]
A.6
B.7
C.8
D.9
答案：B
China’s New Food Act provides for a food recall system to producers have to stop production their food isn’t up to standards.
A．that; if
B．where; if
C．which; when
D．when; where
适用于热结旁流的治则是（）
A.热因热用
B.寒因寒用
C.通因通用
D.塞因塞用
E.寒者热之
