When he died in April of 1983, Dr. Joel Hildebrand was 101 years old, who had been married for seventy-five years, and had taugh

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问题    When he died in April of 1983, Dr. Joel Hildebrand was 101 years old, who had been married for seventy-five years, and had taught freshman chemistry to over 40,000 college students.
   For his life, he had published a popular chemistry textbook and dozens of articles, managed the U. S. Olympic ski team, and discovered a way to allow deep-sea divers to stay underwater longer. In his own way, Dr. Hildebrand was certainly a genius.
   Dr. Hildebrand’s interest in chemistry began at an early age. In an interview, he once said that his interest had been formed because he was fortunate enough to be born before there was television, so he had to make his own decisions about what to pay attention to. Even as a student in high school. Dr. Hildebrand 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. Hildebrand went on to teach at the University of California at Berkeley and remained there for almost forty years.
   During that time, Dr. Hildebrand 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 for deep-sea diving is now standard practice. Dr. Hildebrand 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 snowmobile, a vehicle used to carry soldiers through the snow in northern countries.
   Dr. Hildebrand’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.  Hildebrand’s writing career continued, however, and was still feeling strong at the age of 100, when he published an article on the theory of chemical solutions. Dr. Hildebrand’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."  
The use of helium for deep-sea diving ______.

选项 A、helped to overcome the physical discomforts the divers suffered when nitrogen was used
B、was found by Dr. J. Hildebrand
C、is now still generally acknowledged as standard practice for deep-sea diving
D、may be thought to contain all the information stated in A, B, and C

答案D

解析 见第四段。
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