For thousands of years, people have used plants to make medicines. They used different parts of the plants --the roots, the leaves, the flowers, and the bark  . Today, doctors have rediscovered more medicinal   values of some plants. Let's look at some examples. Foxglove is a common plant. People have used it to make the heart slow down. Recently scientists have developed another drug from it. This new drug helps prevent other heart problems. In some areas, _ has been a problem. Scientists have learned that the bark of a South American tree, the cinchona, can be made into a drug to prevent malaria. For a long time, the Chinese have known that a special plant, wormwood, can also fight malaria. Scientists have been working with it to develop new drugs against malaria. In Germany, some scientists studied garlic   for four years. They found that it helps prevent the build-up of plaque   because too much plaque is bad for health. This very common plant continues to be studied. As we know, there are about 250,000 kinds of flowering plants in the world. Scientists have only studied little more than one percent of plants for their medicinal value. Maybe medicines for AIDS and cancer will be made from the other 99 percent. How many plants are mentioned in the passage?
3. 4. 5. 6