题目

 She ____ the film. She knows nothing about it.    A. can’t see          B. can’t have seen     C. mustn’t have seen     D. must see 答案：B6．从H、O、C、Na四种元素中选择适当的元素，按要求将其适当的化学式填入空格中．（1）用于医疗急救的气体O2；（2）治疗胃酸过多的盐NaHCO3．