شرکت در آزمون آنلاین
زبان انگلیسی 1
-
زبان انگلیسی 1
| آزمون شماره 13950
The average human adult has more than 5 liters (6 quarts) of blood in his or her body. Blood carries oxygen and food to living cells and takes away their rubbish. It also gives safe cells to fight diseases and contains platelets that can form a plug in a damaged blood vessel to stop blood loss.
Through the circulatory system, blood adapts to the body's needs. When you are exercising, your heart pumps harder and faster to provide more blood and also oxygen to your muscles. During an illness, the blood gives more white cells to the site of disease, where they gather to fight and kill the harmful microbes.
All of these functions make blood a valuable liquid. Each year in the USA, 30 million units of blood are transfused to patients who need them. Blood is considered to be so valuable that it is also called "red gold" because the cells and proteins it contains can be sold for more than the cost of the same weight in gold.
The underlined phrase “safe cells” in paragraph 1 refers to … .
In order to collect facts about dinosaurs, we … .
