题目内容：

    Medical developments and discoveries often provide the best things for controversies (争论).This is because whenever a new discovery or theory is proposed, there is always disagreement. Only via objective scientific evidence can such arguments be cleared. But, as is often the case, a clear solution is not instantly found. However, once the technology catches up with the area of the discovery, it shows exactly how valid the theory is. Since this is a slow process and can take years, the development of controversies is unavoidable.

Over the years, various such controversies have been developed, examined, and either rejected, or proved right for the good of mankind. Now read the following examples.

Firstly, cancer was largely regarded as an incurable disease, since its exact cause was unknown. Later, professors and doctors came up with various theories regarding the cause. Some claimed it was the result of chemical processes, while others believed it was a sort of poison. After a few decades, a doctor proposed that cancer was caused by the inhalation (吸入) of pollutants, in the form of smoke, gas, etc. His claim was rejected by many researchers and doctors. However, due to various scientific studies, this claim is now clearly common knowledge, though there may be other causes.

Many people worry that the use of cell phones can cause cancer. Recent studies suggest that this common threat is actually quite true. Numerous studies indicate that the long usage of cell phones (at least an hour per day) increases the risk of developing brain tumors.

After the discovery of X-rays, they were widely used, from doctors' clinics to shoe stores to see the fit of shoes. People thought they could offer the benefit of visualizing the skeleton (骨骼) of a person without causing any danger to the person. However, in 1956, the National Academy of Science reported the harmful effects of these rays on the human body, and the practice was then given up. Presently, we all know that exposure to X-rays may lead to radiation poisoning, tissue breakdown, and even death.

1.What may stop the scientific evidence of a theory being found quickly?

A.Agreement among scientists. B.The lack of professional researchers.

C.Technological limitations. D.The lack of motivation for investigating.

2.Different scientific studies have proved that _________.

A.cancer is not an incurable disease. B.cancer is caused by chemical processes.

C.air pollution is becoming more serious. D.air pollution is one of the causes of cancer.

3.How is the passage mainly developed?

A.By giving examples. B.By making comparisons.

C.By following time order. D.By making classifications.

4.What is the purpose of the passage?

A.To remove people’s misunderstanding of medicine.

B.To report the most recent medical development.

C.To find good solutions to medical problems.

D.To stress the development of controversies.