Passage Three
Nine-year-old Louis Pasteur rushed into the little house, his face white.
"Mother!" he cried, "A mad dog has bitten my friend Henry, and now they are burning him with red-hot irons. It's terrible!"
"Rabies(狂犬病), Louis. Burning the bites is the only hope of stopping Henry from catching the disease."
Henry did get rabies and died, in great pain, some days later. Louis Pasteur never forgot that. "One day," he thought, "I must do something to help people like Henry."
Sixteen years later Pasteur became a Doctor of Science. Arid he began making important discoveries in his special field.
Pasteur achieved great success in his life. But during the years of research he lost the use of his left arm and leg. Yet he worked on and on, as hard as ever, as he was eager to find a way for curing rabies. He never forgot his friend Henry.
After many dangerous experiments on mad dogs, he finally found the answer. Just then a boy who had been badly bitten by a mad dog arrived at his lab. A few days after Pasteur's treatment the boy got better. He did not catch rabies.
The discovery gave new hope to people in many countries. People sent money to help build the Pasteur Institute in Paris. Today it is one the world's most famous centers for research.
44. Pasteur became a Doctor of Science. Doctor of science here means______.

A. a degree which is the highest in science
B. a person who works in the lab
C. a post in science
D. someone whose job is to make sick people well again