[单项选择]

It is bad to have food stuck between your teeth for long periods of time. This is because food attracts germs, germs produce acid, and acid hurts your teeth and gums. Flossing helps to remove the food that gets stuck between your teeth. This explains why flossing helps to keep your mouth healthy, but some doctors say that flossing can be also good for your heart.
It may seem strange that something you do for your teeth can have any effect on your heart. Doctors have come up with a few ideas about how flossing works to keep your heart healthy. One idea is that the germs that hurt your teeth can leave the mouth and travel into your blood. Germs that get into the blood can then attack your heart. Another idea is based on the fact that when there are too many germs in your mouth, the body tries to fight against these germs. For some reason, the way the body fights these mouth germs may end up weakening the heart over time.
Not every doctor agrees about these ideas. So
A. germs from producing acid
B. food from entering your body
C. germs from entering into your blood
D. acid from contacting your teeth and gums

It is bad to have food stuck between your teeth for long periods of time. This is because food attracts germs, germs produce acid, and acid hurts your teeth and gums. Flossing helps to remove the food that gets stuck between your teeth. This explains why flossing helps to keep your mouth healthy, but some doctors say that flossing can be also good for your heart.
It may seem strange that something you do for your teeth can have any effect on your heart. Doctors have come up with a few ideas about how flossing works to keep your heart healthy. One idea is that the germs that hurt your teeth can leave the mouth and travel into your blood. Germs that get into the blood can then attack your heart. Another idea is based on the fact that when there are too many germs in your mouth, the body tries to fight against these germs. For some reason, the way the body fights these mouth germs may end up weakening the heart over time.
Not every doctor agrees about these ideas. So
A. reluctant to hypothesize
B. confident in their estimations
C. extremely knowledgeable
D. uncertain but speculative

Farm animals provide man with food and material for clothing, leather and other products. Some, such as horses and oxen, provide transportation and power to pull machinery. Livestock gaze on about 40 percent of the United States land area.
Cattle provide meat, hides and dairy products. Beef and dairy cattle account for about a third of all farm income in the U.S. Farms in the Midwest and sprawling ranches in the West raise most of the country’s beef cattle. The main Dairy’ Belt in the U. S. extends through the Northern states from New England to Minnesota. Eastern dairy farmers in Minnesota, Wisconsin and Iowa sell most of their milk to companies that make butter, cheese and evaporated milk.
Hogs grow rapidly and provide meat and materials used to make many products. Hogs thrive on corn, and farmers in the Corn Belt of the Midwest raise more than two-third of U. S. hogs.
Sheep and goats supply man with meat, wool and skins for leather. They are
A. horses
B. oxen
C. sheep
D. dairy cows