单选题
{{B}}Passage Five {{/B}} Nutrients are
the parts of food that are important for life and health. Nutrients are
important for three reasons. First, some nutrients provide fuel for energy.
Second, some nutrients build and repair body tissues. Third, some nutrients help
control different processes of the body like the absorption of minerals and the
clotting of blood. Scientists think there are 40 to 50 nutrients. These
nutrients are divided into five general groups: carbohydrates, fats, proteins,
minerals, and vitamins. The first group of nutrients is
carbohydrates. There are two kinds of carbohydrates: starches and sugars. Bread,
potatoes, and rice are starches. They have many carbohydrates. Candy, soft
drinks, jelly, and other foods with sugar also have carbohydrates. Carbohydrates
are important because they provide the body with heat and energy. Sugar, for
instance, is 100 percent energy. It has no other food value. Sugar does not
build body tissues or control body processes. If there are too many
carbohydrates in the body, they are stored as body fat. The body stores fuel as
fat. There are two types of fats: animal and vegetable.
Butter, cream, and the fat in bacon are animal fats. Olive oil, corn oil, and
peanut oil are vegetable fats. The body has fat under the skin and around some
of the organs inside. The average adult has 10 to 11 kilograms (20 to 25 pounds)
of body fat. If adults eat too many carbohydrate and fats, they can add another
45 kilograms (100 pounds) to their bodies. Fat is extra fuel. When the body
needs energy, it changes the fat into carbohydrates. The carbohydrates are used
for energy. Fat also keeps the body warm. The third
group of nutrients is proteins. The word "protein" comes from a Greek word that
means "of first importance". Proteins are "of first importance" because they are
necessary for life. Proteins are made of amino acids, which build and repair
body tissue. They are an important part of all the muscles, organs, skin, and
hair. The body has 22 different amino acids. Nutritionists call eight of these
amino acids essential because the body does not manufacture them.
There are two kinds of proteins: complete proteins and incomplete
proteins. Complete proteins, which the body needs for growth, have all the
essential amino acids. Meat, fish, poultry, eggs, milk, and cheese have complete
proteins. The body needs complete proteins every day. Incomplete proteins do not
have all the essential amino acids. The proteins in vegetables and grains, for
instance, are incomplete proteins. Two ways to form complete proteins from
incomplete proteins are: (1) to mix vegetables and grains correctly, or (2) to
add a small amount of meat or milk to a large amount of grains. The body can
then use the complete proteins which result from the mixtures.
Extra protein in the body can be changed to fat and stored as body fat.
It can also be changed to carbohydrates and used for energy. If people do not
eat enough carbohydrates and fats for the energy that they need, their body uses
proteins for energy. Then the body does not have the proteins that it needs to
build and repair tissues. A nutritious diet includes carbohydrates and fats for
energy, and proteins for growth.
单选题
Carbohydrates are important for______.
A. growth
B. healthy bones
C. energy
D. the clotting of blood
【正确答案】
C
【答案解析】[解析] 从文中第二段中间“Carbohydrates…provide…heat and energy”可知C项正确。