题目

 Mr. Richard was disappointed that many students who had signed up for his adventure course _______ at the last moment. A left out                  B. got out                            C. passed out         D. dropped out 答案：  D在Rt△ABC中，∠C=90°，AC=2cm，BC=4cm，若以点C为圆心，2cm为半径作圆，则点A在⊙C____________，点B在⊙C____________．