题目

下列事件中，是必然事件的是（ ） A . 随意掷一块质地均匀的骰子，掷出的点数是1 B . 射击运动员射击一次，命中10环 C . 掷一块石块，石块下落 D . 在一个装满白球和黑球的袋中摸球，摸出红球 答案：CMary is ill today. If she _____, she _____ absent from school. [     ]A. were not ill; wouldn't be 　　　　　　B. had been ill; wouldn't have been 　　C. had been ill; should have been 　　　　D. hadn't been ill; could be