Scientists have discovered thirteen kinds of vitamins．They say vitamins help to carry out chemical changes within cells．If we do not get enough of the vitamins we need in our food, we are at risk of developing a number of diseases．Which foods should be eaten to keep us healthy? Let us look at some important vitamins．
Vitamin A helps prevent skin and other tissues from becoming dry．People who do not get enough vitamin A cannot see well in darkness．Vitamin A is found in fish liver oil and the yellow part of eggs．
Vitamin B-1 is also called thiamine．Thiamine changes starchy（含淀粉的）foods into energy．Thiamine is found not just in whole grains like brown rice, but also in beans and peas, nuts, and meat and fish．
Vitamin B-12 is needed so folic acid can do its work．Together, they help produce red blood cells．Folic acid has been shown to prevent physical problems in babies when taken by their mothers during pregnancy．Vitamin B-12 is found naturally in foods like eggs, meat, fish and milk products．Vitamin B-12 is found in green leafy vegetables and other foods, like legumes and citrus fruits （柑橘类水果)．
Vitamin C is needed for strong bones and teeth．The body stores little vitamin C．So we must get it every day in foods such as citrus fruits, tomatoes and uncooked cabbage．
Vitamin D prevents the children’s bone disease rickets （佝偻病）．Ultraviolet light from the sun changes a substance in the skin into vitamin D．Fish liver oil also contains vitamin D．
Vitamin K is needed for healthy blood．It thickens the blood around a cut to stop bleeding．It can also be found in pork products, liver and in vegetables like cabbage, kale and spinach （菠菜）．
Vitamins are important to our health．A lack of required vitamins can lead to health problems．
1．What is the main idea of the passage?
A．There are thirteen kinds of vitamins in total．
B．One can not live without enough vitamins．
C．Vitamins can carry out chemical changes within cells．
D．Enough vitamins are vital to keep healthy．
2．Women who wish to become mothers should take in ________．
3．What can change a substance in the skin into vitamin D?
A．Fish liver oil．
B．Ultraviolet light from the sun．
C．Fresh milk drunk by people．
D．Doing a certain amount of exercise．
4．According to the passage, taking in enough vitamin C can ________．
A．make our eyesight better
B．help to stop bleeding
C．make our bones and teeth strong
D．help produce red blood cells
Is It Worth Buying Organic Food?
Organic food，grown without artificial chemicals，is increasingly popular nowadays．Consumers have been willing to pay up to twice as much for goods with organic labels (商标)．However，if you think paying a little more for organic food gets you a more nutritious and safer product，you might want to save your money．A study led by researchers at Stanford University says that organic products aren't necessarily more nutritious，and they're no less likely to suffer from disease-causing bacteria，either．
The latest results，published in the Annuals of Internal Medicine，suggest that buyers may be wasting their money．"We did not find strong evidence that organic food is more nutritious or healthier，" says Dr．Crystal Smith-Spangler from Stanford．"So consumers shouldn't assume that one type of food has a lower risk or is safer．"
For their new study，Smith-Spangler and her colleagues conducted a review of two categories of research，including 17 studies that compared health outcomes between consumers of organic against traditional food products，and 223 studies that analyzed the nutritional content of the foods，including key vitamins，minerals and fats．
While the researchers found little difference in nutritional content，they did find that organic fruit and vegetables were 20% less likely to have chemicals remaining on the surfaces．Neither organic nor traditional foods showed levels of chemicals high enough to go beyond food safety standards．And both organic and traditional meats，such as chicken and pork，were equally likely to be harmed by bacteria at very low rates．The researchers did find that organic milk and chicken contained higher levels of omega-3 fatty acids，a healthy fat also found in fish that can reduce the risk of heart disease．However，these nutritional differences were too small，and the researchers were unwilling to make much of them until further studies confirm the trends．
Organic food is produced with fewer chemicals and more natural-growing practices，but that doesn't always translate into a more nutritious or healthier product．The U．S．Department of Agriculture (USDA) states that "whether you buy organic or not，finding the freshest foods available may have the biggest effect on taste．" Fresh food is at least as good as anything marketed as organic．
1．The new research questions whether organic food __________．
A．should replace traditional food
B．has been overpriced by farmers
C．is grown with less harmful chemicals
D．really more nutritious and healthier
2．Smith-Spangler and her colleagues found that __________．
A．organic food could reduce the risk of heart disease
B．traditional food was grown with more natural methods
C．both organic and traditional food they examined were safe
D．there was not a presence of any forms of bacteria in organic food
3．Which of the following is relatively healthier according to the passage?
A．Organic chicken and pork．
B．Organic milk and chicken．
C．Traditional chicken and pork．
D．Traditional fruit and vegetables．
4．What is the author's attitude toward organic food?