更多"Scientists have learned a great dea"的相关试题:
[单项选择]Scientists have learned a great deal about the kinds of food people need. They say that there are several kinds of food that people should eat every day. What are these classes of food They are 1) green vegetables of all kinds, such as string beans, peas, lettuces, and cabbages; 2) fruit, such as apples, peaches and bananas; 3) other vegetables, examples of these are beets, onions, carrots, tomatoes and so on; 4) meat of all kinds, fish and eggs; 5) milk and food made from milk, such as butter, cheese and ice-cream; 6) bread or cereal. Rice is also in this class of food.
People in different countries and different areas of the world eat different kinds of things. Scientists say that none of these differences are really important. It doesn’t matter whether food is eaten raw or cooked, canned, or frozen. It doesn’t matter if a person eats dinner at four o’clock in the afternoon or at eleven o’clock at night. The important thing, they say, is that every day a person should eat someth
A. The kinds of food that should be eaten every day.
B. Whether to eat food raw or cooked.
C. When to eat food every day.
D. How much food to eat every day.
[简答题] Scientists have learned more about the way cancer spreads from one place in the body to another. Once it spreads, it gets more difficult to treat. Cancer is a disease of uncontrolled cell growth. Traditional thinking is that cells simply break off the main cancer, travel through the blood and grow in other organs.
But the new findings suggest there is more to this process. Researchers found that cells from the main tumor send out messengers. These prepare the new organ for a secondary tumor (瘤). It works this way. The primary tumor releases proteins called growth factors into the blood. They signal cells at the target organ to produce a sticky protein, called fibronectin. It attaches to the surface of bone marrow (骨髓) cells. The result is a kind of landing area for cancer to arrive and grow into a secondary tumor.
The bone marrow cells help make vessels for blood to pass through and feed the cancer cells. The researchers believe that without the bone marrow cells, the tum