For thousands of years humans have used herbs, roots, and other things from nature to cure disease. Scientists looking for new cures often visit traditional healers. They find out what plants are used in healing. Then they look at what the plant contains. They find the active ingredient, which is the chemical in the plant that works to heal. Many of the drugs we use, including aspirin, have come from these natural medicines.

In recent years, many people in the US have been taking what are legally known as dietary supplements（补药）. They may be vitamins or minerals. They may be herbs that help with health problems, such as depression. Some of them are teas. Others are capsules or tablets. They are sold in natural food stores, drug stores, and groceries. Most people think that because these products are natural they are also safe. This is not always true. There are many plants that are poisonous. There are others that have bad side effects.

The New England Journal of Medicine publishes medical research. A recent edition called for the government to regulate dietary supplements. Several doctors wrote to the Journal and told of bad experiences people have had with dietary supplements.

Dietary supplements aren't tested in the same way as drugs. There is not always proof that the supplement really does what it is supposed to do. There is also a problem with purity of the supplements. Supplements have been found to contain things that are bad for the body. For example, the California Department of Health found that of 260 herbs grown in China, one third contained heavy metals. These are minerals such as lead and mercury（水银）. They are very poisonous, even in tiny amounts.

1. The scientists study the cures from the healers in order to _______.

   A．find out if the plant is poisonous

   B．find out what in the plant works to cure disease

   C．look for aspirin in the plant

   D．make sure that the plant can cure disease

2. We can infer from the second paragraph that _______.

   A．it is legal to take dietary supplement in the USA

   B．supplements are safe because they are natural medicines.

   C．all the supplements are poisonous

   D．none of the supplements has bad side effects

3. The underlined word “regulate” in the third paragraph means _______.

   A．punish          B．remove        C．control          D．manage

4. Which one of the following is NOT right according to this passage?

   A．Scientists think herbs, roots can be used to cure disease.

   B．People believe dietary supplements contains vitamins and minerals.

   C．It is right that the dietary supplements are always safe.

   D．Dietary supplements are harmful to your health.