题目

--- An explosion at a coal mine killed at least 62 workers and left another 13 missing. --- Yes,               news came as       shock to us all. A. the; the                B. /; /         C. /; a       D. the; a 答案：D如图，已知Rt△ABC，∠ABC=90°，以直角边AB为直径作⊙O，交斜边AC于点D，连接BD．（1）若AD=3，BD=4，求边BC的长；（2）取BC的中点E，连接ED，试证明ED与⊙O相切．