题目

 She had just finished her homework ____ her mother asked her to practise playing the piano yesterday. A.when              B. while             C. after            D. since 答案：A在△ABC中，若∠A∶∠B∶∠C=1∶2∶3,则a∶b∶c等于  A.              B.           C.      D.1∶∶2