通常的食醋中约含3%～5%的乙酸（化学式为C2H4O2）．有关乙酸的说法，正确的是（ ）
A．乙酸是一种氧化物
B．乙酸中碳、氢元素的质量比为6：1
C．乙酸中碳元素的质量分数为10%
D．乙酸含有2个碳元素、4个氢元素、2个氧元素
答案：B
题目分析：A、乙酸是由碳、氢、氧三种元素组成的，不属于氧化物，故选项说法错误．
B、乙酸中碳、氢元素的质量比为（12×2）：（1×4）=6：1，故选项说法正确．
C、乙酸中碳元素的质量分数为
100%=40%，故选项说法错误．
D、元素只讲种类、不讲个数，乙酸中含有碳元素、氢元素、氧元素，故选项说法错误．
故选B．
点评：本题难度不大，考查同学们结合新信息、灵活运用化学式的含义与有关计算进行分析问题、解决问题的能力．
| Few creatures on earth are as cute as the black lion tamarin, and few have as dramatic a story line. Pug-nosed and diminutive, with a comic fringe of hair, these monkeys dwell in trees in small tracts of forest in southeastern Brazil. Or they did until 1905, when they were declared extinct. No one saw a black lion tamarin again in the wild until 1970. Later, in the 1990s, some Brazilian researchers turned up a small set of isolated, inbred populations scattered over a wide region. Since that time, they have been engineering tamarin migration, doing everything they can to save the world’s most distinctive primates. Although they are no larger than house cats, tamarins have brains big for their size and a family life organized like our own. They live in groups anchored by an adult male andadult female, along with their offspring. When a mother bears young, she usually produces twins, and although members of the group share in their upbringing, it is most often the father who carries them around in the trees, where the families feed on fruits, insects and bird’s eggs. Unhappily for the lion tamarins, their tree-bound niche began to disappear after the Portuguese landed in Brazil and began clearing forest to make room for Rio de Janeiro, the settlements and farms. As is the case for so many threatened species, the breakup of their habitat sounded the death knell for tamarins, depriving them of the continuity of forest they require to remain abundant and safe from potential threats in any single vicinity. The animals avoid predators by hardly ever coming down from the trees, so even a narrow logging road through a forest can begin the breakup by preventing them from moving from one patch of forest to another. A simple solution was to build bridges across roads, allowing the monkeys to move from one forest to another. With some lumber and the researchers’ work, habitats that had been separated became continuous again, improving opportunities for migrating and mating. The next step was to broaden the distribution of the population. The researchers captured two families of black lion tamarins and moved them to a new forest. After a year, the moves were declared a success: Not only had 80 percent of the tamarins survived, but they had also produced new offspring. So far, so good. The researchers had learned the animals could adjust to the new habitats, even if the insects there tasted a little different or the trees were a slightly different size. The techniques for saving species in the wild vary. Species with less stringent habitat requirements, like wild turkeys, have been rescued by moving them into new settings as well as outlawing their killing. More challenging to preserve are species that require a lot of land, like elephants, and species that have highly specific requirements for habitat and prey -- like black-footed ferrets. Ultimately, as in all challenges, knowledge is power to save wild species from extinction. |
Tamarins lost the paradise of their tree-bound niche mainly because the Portuguese ______.
A．cut down trees to make rooms of the houses
B．cleared the forests to set up cities and farms
C．deforested some regions for playgrounds
D．hunted the most distinctive monkeys