问题 选择题

物质间存在着一定的反应关系和转化关系.下列各组物质可以按所给图示进行直接转化的是(  )

A.Fe→Fe2O3→FeSO4→Fe

B.CO→CO2→H2CO3→CO

C.HCl→NaCl→CaCl2→HCl

D.CO2→Na2CO3→CaCO3→CO2

答案

A、Fe2O3→FeSO4不能一步实现,只能和稀硫酸一步生成硫酸铁.

B、H2CO3→CO不能一步实现,只能一步分解生成CO2

C、NaCl→CaCl2不能一步实现,因为根据复分解条件可知,要生成CaCl2,必须是和钙离子的盐或碱反应,但钠离子的盐或碱都是可溶于水的,所以不能发生复分解反应;

D、反应流程为:CO2+NaOH→Na2CO3;Na2CO3+CaCl2→CaCO3;CaCO3→分解生成CO2,所以正确.

故选D

单项选择题
阅读理解

Now, we know that if we do not get enough vitamins, we are at risk of developing a number of diseases. As a result, vitamin supplements(补品),though expensive, are popular with people who worry that they are not getting enough vitamins from the foods they eat. But contrary to what many people think, medical experts have found little evidence that most supplements do anything to improve health or protect against disease.

In fact, medical experts warn that taking too many of some vitamins can be harmful. For example, too much vitamin E can cause bleeding. People should discuss what vitamins they take with their doctors, as some vitamins can produce harmful side effects when mixed with medicines.

Experts, however, do say that sometimes vitamins can help prevent disease. People who know they lack a particular vitamin should take vitamin supplements. Some older adults, for example, may not have enough vitamin B-twelve. This is because, as people get older, their body loses its ability to take it from foods. Also, people who spend much time inside may need some extra vitamin D as the skin makes this vitamin from sunlight.

Different vitamins are found in different foods. Vitamin A is found in fish liver oil. It also is in the yellow part of eggs. Sweet potatoes, carrots and other darkly colored fruits and vegetables contain substances that the body can change into vitamin A. Vitamin B-twelve is found in green leafy vegetables and other foods, like fruits. Vitamin K can be found in pork products.

In fact, for most people, a balanced diet can ensure enough of the vitamins our bodies need. So, it is important for us to eat a mixture of foods every day to ensure that we get enough vitamins our bodies need.

小题1:Vitamin supplements are popular with people because ________. 

A.people mistakenly think that they are good for their health

B.they contain more vitamins than the foods people eat

C.food does not provide enough vitamins people need

D.people fear that a lack of vitamins will lead to disease小题2:From the passage, we can learn that medical experts advise people _________.

A.never to take any vitamin supplements

B.to depend only on food for their vitamins

C.not to take any vitamins together with medicines

D.to consult doctors before taking vitamin supplements小题3:For people who lack Vitamin B-twelve, they can eat more from _______.

A. sweet potatoes   B. pork products   C. green leafy vegetables  D. eggs

42. What would be the best title of the passage?

A. Getting enough vitamins through a balanced diet.

B. Vitamin supplements do harm to our health.

C. Vitamins are important to our health.

D. Lacking vitamins can cause many diseases.