题目

如图，将△ABC绕点A逆时针旋转一定角度，得到△ADE．若∠CAE=63°，∠E=72°，且AD⊥BC，则∠BAC的度数为（ ）A. 63° B. 72° C. 81° D. 85° 答案：【答案】C【解析】根据旋转的性质知，∠EAC=∠BAD=63°，∠C=∠E=72°.如图，设AD⊥BC于点F. 则∠AFB=90°，∴在Rt△ABF中，∠B=90°−∠BAD=27°，∴在△ABC中，∠BAC=180°−∠B−∠C=180°−27°−72°=81°，即∠BAC的度数为81°.故选：C.- Why? Tom, your shirt is so dirty!- Mum, I ＿＿ my storeroom downstairs。 A. cleaned　 B. have worked C. was cleaning 　 D. have been cleaning