题目

I _    _ cleaning the house by 4:30 yesterday afternoon .           A. had finished     B. finished      C. have finished    D. finish 答案：A如图，在△ABC中，∠C=90°，∠A=30°，AB=2，D为AB的中点，DE⊥AB交AC于点E，连接BE，则△ABE的面积等于    ．