题目

— Lucy didn’t come to school , did she? — __________ . She was ill in bed. A.No,she did. B. No, she didn’t C. Yes, she did. D. Yes, she didn’t.     答案：B设甲、乙、丙三人每次射击命中目标的概率分别为0.7、0.6和0.5。三人各向目标射击一次，求至少有一人命中目标的概率及恰有两人命中目标的概率。