阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。
No one is glad to hear that his body has to be cut open by a surgeon (外科医生) and part of it taken out. Today, however, we needn't worry about feeling pain during the operation. The sick person falls into a kind of sleep, and when he awakes, the operation is finished. But these happy conditions are fairly new. It is not many years since a man who had to have an operation felt all its pain.
Long ago, an operation had usually to be done while the sick man could feel everything. The sick man had to be held down on a table by force while the doctors did their best for him. He could feel all the pain if his leg or arm was being cut off, and his fearful cries filled the room and the hearts of those who watched.
Soon after 1770, Josept Priestley discovered a gas which is now called “laughing gas”. Laughing gas became known in America. Young men and women went to parties to try it. Most of them spent their time laughing. But one man at a party, Horace Wells noticed that people didn't seem to feel pain when they were using this gas. He decided to make an experiment on himself. He asked a friend to help him. Wells took some of the gas, and his friend pulled out one of Wells' teeth. Wells felt no pain at all.
