Câu hỏi:

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  Antioxidants are substances – artificial or natural – that prevent and slow cell and tissue damage by attacking free radicals. which are molecules that have an unpaired electron. Free radicals are natural byproducts of our metabolism and are also generated in response to environmental stressors, such as exposure to pollution, X-rays or cigarette smoke. In high quantities. free radicals can cause oxidative stress, which is when the body has too many free radicals that stat to destroy DNA, fatty tissue and proteins. [A]     Unlike free radicals, antioxidants have extra electrons. This means that they can pass their surplus electrons lo free radicals, stabilizing the free radicals so they can no longer damage the body's cells and tissues. In doing so, antioxidants ward off or slow oxidative stress, preventing serious illnesses. Oxidative stress bas been linked with illnesses such as cancer, heart disease and some neurodegenerative diseases, including Alzheimer's and Parkinson's disease. The best way 10 increase antioxidants in the body and maintain a healthy balance of free radicals is to incorporate antioxidant-rich foods into your diet. [B]     The term ·antioxidant' is often used to describe different foods, but it more accurately describes chemical property. Any substance that can strip free radicals of their damaging properties is considered an antioxidant. Researchers have discovered hundreds of substances that fit the antioxidant description, and there are perhaps thousands more. Vitamin C and vitamin E are two of the most common antioxidants found in food. In addition to fighting free radicals, vitamin C supports the immune system and helps repair bones, teeth and cartilage. Vitamin E is a powerful tool in maintaining eye health, producing hormones that regula1e blood pressure and repairing muscles after exercise. Carotenoids- a class of compounds found in fruits and vegetables that are red, orange and yellow - are also well-known antioxidants. Antioxidant carotenoids include beta-carotene, lycopene, lutein and zeaxanthin. However, taking high doses of some carotenoid supplements, such as beta-carotene. can increase health risks, such as an increased chance of lung cancer in smokers. [C]     Antioxidants are most often in fruits, vegetables and legumes, although they can be found in almost every food group. Fruits contains essential nutrients such as potassium, fibre and folate - nutrients that help maintain blood pressure, lower cholesterol and repair body tissues. Blueberries, cranberries, apples, strawberries and more are all filled with antioxidants. Dried fruits - although often high in processed sugars - have a higher antioxidant ratio than fresh fruits, since they lose mass from water. They act as quick antioxidant fuel due to their high concentration of antioxidants. Carotenoids are found in red, orange or yellow vegetables. Many green vegetables such as kale, broccoli and spinach are excellent sources of antioxidants, namely quercetin and lutein. [D]

According to the passage, which of the following is true about free radicals?