题目

（本题满分8分）如图，AB是⊙O的直径，过B点作⊙O的切线，交弦AE的延长线于点C，作，垂足为D，若，，求DE的长．  答案：解法一：∵BC是⊙O的切线，     ∴．在Rt△ABC中，∵， ∴．∴．··············································································· 3分在Rt△AOD中，， ∴．···· 6分∵，   ∴．·············································�下列各组物质中，前者为附着在容器内壁的物质，后者为选用的洗涤剂．其中搭配不合适的是 [　　] A．银镜，氨水B．油脂，热碱液 C．石蜡，汽油D．晶体碘，酒精