Louis Pasteur, one of the world's great scientists, was born in 1822, and died in 1895.While still a young boy, Louis Pasteur made his decision to become a scientist. He spent much of his life time studying the diseases of cattle, chickens and other tame animals. His wife learned to help him with his work. Almost everyone knows that Pasteur is the man responsible for finding a way of preventing milk from spoiling  . Not many people know he was the first to imagine and to prove that air we breathe is full of germs  .  One of his greatest successes was finding a treatment for people and animals to prevent a disease called rabies  . Louis Pasteur won many honors and could have got large amount of money. But Pasteur preferred to live simply. The real happiness of this unusual man came from his work. Louis Pasteur did so well in his life that the French government took up his work and created the Institute Pasteur in the year 1888. From the passage, we know that Pasteur lived a simple life. This is because   _  .
he earned little money. he cared much about money. what he really enjoyed was a simple life. of all mentioned above.