“可燃冰”〔CH4·(H2O)n〕是在海底的高压低温条件下形成的，外观像冰，下面关于“可燃冰”叙述正确的是
A．CH4·(H2O)n 是氧化物
B．“可燃冰”是一种比较清洁的能源
C．“可燃冰”提供了水可能变成油的证据
D．“可燃冰”可直接拿回家作为燃料使用
答案：B
A、氧化物是由两种元素组成其中一种为氧元素的化合物，可燃冰中含有碳、氢、氧三种元素，故不是氧化物，说法错误；
B、因为甲烷燃烧产物是二氧化碳和水，所以不污染环境，所以“可燃冰”是一种比较清洁的能源，故正确；
C、可燃冰可燃烧部分是甲烷，根本不会变成油，故错误；
D、可燃冰能燃烧的部分是甲烷，需经处理后使用，所以错误．
故选B
I break off a piece of candy and take pleasure in its sweet outside and the bitter, dark chocolate inside, thinking of my own life. Being raised by a single parent was a bitter-sweet , which gave me motivation and ambition. There were several years that have left an extremely bitter taste in my mouth .The first few months after my mother’s remarriage were sweet: baseball games, family trips to the mall, dinners and movies together. Then things . Baseball became too expensive, and trips to the mall were by days Emily and I spent lonely in our rooms under our stepfather’s . Moreover, screaming matches between him and our mother always dinner. We spent five years living in a family that had a war field. Emily and I almost grew used to this situation. Then one evening, after another argument had , we were left homeless . And later a friend of my mother let us stay with her. Instead of focusing on our economic problem, my mother pushed me to struggle for success. She wanted me to lead a life. She worked long hours every night to pay her bills. , she would find time to read and play with Emily and me. Mom taught me the of perseverance (坚持不懈) and education. And now, writing this essay with my favorite candy close at hand, I realize my family and I are at the best points of our lives. I haven’t let the trying times stop me from making , both academically and personally. I know that a bitter environment can provide good learning experiences, and that success, even more than candy, is the sweetest treat of all.
|
收敛性的结论中，正确的是（）。