Part A
Directions: Read the following four texts. Answer the questions below each text by choosing A, B, C or D. Mark your answers on ANSWER SHEET Ⅰ.
Text 1
Say the word bacteria, and most folks conjure up images of a nasty germ like staphylococcus or salmonella that can make you really sick. But most bacteria aren't bad for you. In fact, consuming extra amounts of some bacteria can actually promote good health. These beneficial bacteria are available without a prescription in drug and health-food stores and in foods like yogurt. So far, the best results have been seen in the treatment of diarrhea, particularly in children. But re searchers are also looking into the possibility that beneficial bacteria may thwart vaginal infections in women, prevent some food allergies in children and lessen symptoms of Crohn's disease, a relatively rare but painful gastrointestinal disorder.
So where have these good germs been lurking all your life？ In your intestines, especially the lower section called the colon, which harbors at least 400 species of bacteria. Which ones you have depends largely on your environment and diet. An abundance of good bacteria in the colon generally crowds out stray bad bacteria in your food. But if the bad outnumber the good—for example, after antibiotic treatment for a sinus or an ear infection, which kills normal intestinal germs as well—the result can be diarrhea.
For generations, people have restored the balance by eating yogurt, buttermilk or other products made from fermented milk. But nowadays, you can also down a few pills that contain freeze-dried germs. These preparations are called probiotics to distinguish them from antibiotics. Unfortunately, you can't always be sure that the bacteria in the products you buy are the same strains as those listed on the label or even that they're still alive. Probiotics are usually sensitive to both heat and moisture. Among the most promising and most thoroughly researched probiotics is the GG strain of Laetobacillus, discovered by Dr. Sherwood Gorbach and biochemist Barry Goldin, both at Tufts University School of Medicine. L-GG, as it's called, has been used to treat traveler's diarrhea and intestinal upsets caused by antibiotics. Even more intriguing, L- GG also seems to work against some viruses, including rotavirus, one of the most common causes of diarrhea in children in the U. S. and around the world. Here the effect is indirect. Somehow L-GG jump-starts the immune system into recognizing the threat posed by the virus.
Pediatricians at Johns Hopkins are studying a different bug, the Bb-12 strain of Bifidobacterium, which was discovered by researchers at CHR Hansen Biosystems. Like L-GG, Bb-12 stimulates the immune system. For reasons that are not dear, infants who are breast-fed have large amounts of bifidobacteria in their intestines. They also have fewer intestinal upsets. Dr. Jose Saavedra and colleagues at Hopkins have shown that Bb-12 prevents several types of diarrhea, including that caused by r0tavirus, in hospitalized infants as young as four months. It has also been used to cure diarrhea in children of all ages.
21. What the author mainly intends to say in the first paragraph is ______.

A. that nasty germs can make you really sick
B. that the word bacteria doesn't refer to the germs which make people sick
C. the beneficial effects that most bacteria may produce on human body
D. the possibility that beneficial bacteria may stop vaginal infections in women