有一包固体混合物溶于水，发现有难溶物质存在，加入过量的稀硝酸后，仅有一部分沉淀消失．符合上述试验现象的固体混合物是（ ）
A．K2CO3Ba（NO3）2（NH4）2SO4
B．NaSO4BaCl2KNO3
C．BaCl2Mg（NO3）2NaOH
D．AgNO3Cu（OH）2Zn（NO3）2
A、中的三种物质在水中溶解后，会生成硫酸钡沉淀和碳酸钡沉淀，加入硝酸后，碳酸钡沉淀会溶解，而硫酸钡沉淀不会溶解，故A正确，
B、中的三种物质在水中溶解后，只会会生成硫酸钡沉淀，加硝酸后，沉淀不会溶解，故B错误，
C、中的三种物质在水中溶解后，会生成氢氧化镁沉淀，加入硝酸后，氢氧化镁沉淀全部会溶解，故C错误，
D、中的三种物质不会反应，加硝酸后，氢氧化铜沉淀全部溶解，故D错误，
故选A．
Directions：For each blank in the following passage there are four words or phrases marked A，B，C and D．Fill each blank with a word or phrase that best fits the context． In the past, man didn’t have to think about the protection of his environment. There were few people on the earth, and natural resources seemed to be 36 . Today things are 37 , and the world has become too 38 . We’re using up our natural resources too quickly, and at the same time we are 39 our environment with dangerous chemicals. If we continue to do this, human life on the earth will not survive. Everyone 40 today that if too many fish are taken from the sea, there will soon be none left. Yet, with modern fishing 41 , more and more fish are caught. We know that if too many trees are cut down, forests will disappear and nothing will grow on the land. Yet, we 42 to use bigger and more powerful machines to cut down more and more trees. We know that if rivers are polluted with waste products from factories, we’ll die. 43 , in most countries wastes are still put into rivers or into the sea, and there are 44 laws to stop this. We know, too, that if the 45 of the world continues to rise at the present rate, in a few years there will not be enough food . What can we do to solve these problems? If we eat more vegetables and less meat there will be more food available for every one. Land that is used to grow crops 46 five times more people than land where animals are kept. Our natural resources will last longer if we learn to recycle them. The world population will not rise so quickly if people use modern methods of birth control. Finally, if we educate people to think about the problems, we shall have a better and cleaner 47 in the future.
|