案例分析题
Bacteria are terribly good for you. So say the promoters of a rapidly growing industry in "probiotic" products. The title "probiotic" (for life) is technically reserved for those food products containing living cultures of "good" microorganisms. Just how good are they It depends on to whom you are listening.< br>"Microbic marketing" is highly competitive; many brands of yogurts, many yogurt drinks, and many capsules of live bacteria are on display -all promising to be good for you ! Promotions are intense, and the questions are many. Do healthy people need cultures of bacteria when they already have a crowd of fine bacteria at work How valid are the claims that probiotic products increase the health of intestinal cells, degrade toxins, or prevent cancer There is yet no scientific consensus, and for now, consumers must decide for themselves.< br>The recent interest in probiotic products has grown out of a concern for the side effects of antibiotics in the 1950s. Since antibiotics are not very selective as to which bacteria they attack, those prescribed for a toothache can quickly wipe out a whole population of intestinal microbes. Bacteria contained in fermented-milk products appeared to be effective in restoring populations of the beneficial bacteria after such a catastrophe. In the development of probiotic products, different species of Lactobacilli and Bifidobacteria are selected according to their abilities to produce yogurt, to survive passage through the digestive tract, and to establish themselves in their new environment by out-competing potentially unfriendly microbes for space and nutrients. This last criterion is not always easy to measure.< br>Cultures of yogurt must contain at least 100 million live bacteria per gram. It’s a big number, but it is impossible to know how many will loiter in your digestive system. Research now is underway to determine whether probiotic products might take the place of controversial antibiotics in livestock feed, or if bacterial/antibacterial compounds might be useful as food preservatives. Probiotics is about using bacteria to control other bacteria!< br>
Which category of writing does the passage belong to（）
A. Narration. < br> B. Description. < br>C. Exposition. < br> D. Argumentation.
