题目

一How do you learn English so well? 一__________chatting with my uncle in America online． A．For       B．By       C．In        D．With 答案：B在矩形ABCD中，两条对角线AC、BD相交于O，∠ACB=60°，AD=4（1）判断△AOD的形状；（2）求对角线BD的长及AB的长．