【单选题】-----His plan sounds ____ , doesn’t it? -----But it is difficult to ____
【简答题】航空器一般可飞行在地球大气环境的________层和________层。
【判断题】蘑菇、香菇、银耳则含有皂甙类物质,具有提高人体免疫功能和抗肿瘤的作用。
【简答题】航空器一般可飞行在地球大气环境的________层和________层。
【单选题】Your plan, as well as his, sounds original. But the company, I think, won't approve _____ of them, for they are unrealistic. [ ]