题目

阅读下面短文，根据所给情节进行续写，使之构成一个完整的故事。I know what courage looks like. I saw it on a flight I took six years ago, and only now can I speak of it without tears filling eyes at the memory.When our L3011 left the Orlando airport that Friday morning, we were a high-energy group. The early-morning flights hosted mainly professional people going to Atlanta for a day or two of business. And a couple of rows to my left, a seemingly 6-year-old kid nestled in her mother's arms.Immediately the aircraft took off, and it was clear that something was wrong 如图，AB是⊙O的直径，AM为弦，∠MAB=30°，过M点的⊙O的切线交AB延长线于点N．若ON=12cm，则⊙O的半径为    cm．