Joseph Goldberger was a doctor for the Unite States Public Health Service. In 1912，he began to study a disease that was killing thousands of people in the South. The disease was pellagra（烟酸缺乏病）.
Doctor Goldberger traveled to the state of Mississippi where many people had pellagra. He studied the patients and their families. Most of the people were poor. The doctor came to believe that the disease was not passed from one person to another, but instead had something to do with food.
He received agreement from state officials to test this idea at a prison（监狱）. Prisoners were offered pardons if they took part. One group of prisoners received their usual food, mostly corn. A second group ate meat, fresh vegetables and milk. Members of the first group developed pellagra. The second group did not.
But some experts refused to accept that poor food caused pellagra. They thought there were other causes.
So Doctor Goldberger put blood from a person with pellagra into his own body. He even took pills that had blood from pellagra patients. An assistant also took part in the experiments. So did Doctor Goldberger's wife. None of them got sick. Later, the doctor discovered that a bit of dried brewer's yeast （酿酒的酵母）each day could prevent pellagra.
Joseph Goldberger died of cancer in 1929. He was 55 years old. Several years later, researchers discovered the true cause of pellagra ： having little of the vitamin B.
How old was Doctor Goldberger when he began to study pellagra?

A．22.

B．30.

C．38.

D．55.

The underlined words " this idea" （in Paragraph 3） refers to __________.

A．the guessing that pellagra had something to do with food

B．a kind of yeast that prevented pellagra

C．pellagra that was easily passed from one person to another

D．a poor food that caused pellagra

Which is the right order about what Doctor Goldberger did?
a. He did a test on prisoners at a prison.
b. He did the experiments on himself.
c. He came to Mississippi to study the patients and their families.
d. He found poor food was easy to cause pellagra.
e. He discovered a little dried brewer's yeast every day could prevent pellagra.

A．a, d，c, e，b

B．c, a，d, b，e

C．b, e，c, a，d

D．c, b，e, a，d

This passage mainly tells us __________.

A．Doctor Goldberger's life

B．something about pellagra

C．Doctor Goldberger's work experience

D．Doctor Goldberger's study on pellagra