If the ratio of the degree of exterior angleof ∠A,∠B and ∠C that are in the triangleABC is 5:4:3,then the ratio of the degree of ∠A,∠B and ∠C is ( )A、5:4:3 B、3:4:5 C、1:2:3 D3:2:1 答案: 解析:略 如图:Rt△ABC中,∠ACB=90°,CD是高,AC=4cm,BC=3cm,则CD=( )A.5cmB.125cmC.512cmD.43cm