A:生物的生活需要营养
B:生物能排除体内产生的废物
C:生物能进行呼吸
D:生物能对外界刺激作出反应
— I don’t like this kind of clothes because it is out of date.
—Never mind. There are many new ones. Please come here to have a look.
设是各项为正数的无穷数列,Ai是边长为ai,ai+1的矩形面积(i=1,2,...),则{An}为等比数列的充要条件为( )