题目

It’s so beautiful outside that spending the day in the office would be very boring. So why not take the vacations(假期)off? A new survey(调查)found that 31﹪of U.S workers don’t always take all of their vacation days. Americans have 12 vacation days on average(平均)each year, but they give back an average of 3 vacation days each year. So why don’t they use up their vacation days? Some say they would rather get money back for their unused days; some busy workers say they just can’t leave their work. Americans have fewer vacation days than workers in any other country sur欧洲“火星快车”探测器和美国的“勇气”号和“机遇”号孪生火星探测器成功登上火星后，相继探测到火星上有水存在的可能，使人类探索自己星球以外的高级生命和追求地球外栖息地的愿望将有可能成为现实。下列关于水与生命关系的叙述错误的是 (    )A．各种生物体的一切生命活动，不能离开水 B．水在细胞内以自由水和结合水两种形式存在C．自由水是组成细胞结构的重要成分 D．自由水参与细胞中各种代谢作用