When he died in April of 1993, Dr. Jeol Hiderbrand was 101 years old, had been married for

seventy years, and had taught freshmen chemistry to over 40,000 students. In addition, he had published a popular textbook and dozens of articles, had managed the U.S. Olympic ski team, and had discovered a way to allow deep-sea divers to stay underwater longer. In his own way, Dr. Jeol Hiderbrand was certainly a genius.

Dr. Jeol Hiderbrattd's interest in chemistry began at an early age. In an interview, he once said that his interest formed because he was fortunate enough to be born before there was a television, so he had to make his own decisions about what to pay attention to. Even as a student in high school, Dr. Jeol Hiderbrand had the reputation as the one who learned more chemistry than his teacher knew. As a result he was given the keys to the high school chemistry lab, and there he discovered that the correct formula for a certain chemical compound was not the one given in his chemistry book but a totally different one. Dr. Jeol Hiderbrand went on to teach at the University of California at Berkeley and remained there for almost forty years.

During that time, Dr. Jeol Hiderbrand discovered that the gas helium could be combined with oxygen for use as diving gas to allow divers to dive deeper and take the great pressure of the water without the physical discomforts that had been experienced when they used another gas, nitrogen. The use of helium (氦气) for deep-sea diving is now standard practice.

Dr. Jeol Hiderbrand was also valuable to his country during both World Wars. In World War I he analyzed the poisonous gases used on the battlefield and helped develop a truck that could clean and treat soldiers' clothes, which had been contaminated by poisonous gases during fighting. In World War Ⅱ, he helped develop a type of the snowmobile, a vehicle used to carry soldiers through the snow in northern countries.

Dr. Jeol Hiderbrand's retirement from teaching at the age of seventy was required by state law in California. He objected to this, joking that he thought a teacher's time of retirement ought to be determined not by age but by how many of that teacher's students were still awake after the first fifteen minutes of class! Dr. Jeol Hiderbrand's career continued, however, and was still going strong at the age of 100, when he published an article on the theory of chemical solutions. Dr. Jeol Hiderbrand's love of life and his interest in it were an inspiration to all who knew him. When asked once how he could have such ageless energy and vigor, he said, "I chose my ancestors carefully.

Which of the followings is the main idea of the passage？

A．Dr. Jeol Hiderbrand's discoveries and inventions.

B．Dr. Jeol Hiderbrand's contributions to education.

C．Dr. Jeol Hiderbrand's contributions to the world.

D．Dr. Jeol Hiderbrand, a versatile with ageless energy and vigor.