A warm-hearted (热心的) nurse on her first day’s work went near to a patient. He has come to London as a tourist. She asked him if she could do something for him, but he only waved (摇) his hand and said something she could not understand. With a smile, she asked him again and he just kept saying the same word but in a much lower voice before closing his eyes. She went to the doctor and repeated (重复) to him the sounds she had heard. "My dear girl, " said the doctor after listening carefully to what she repeated, he was saying, "You are standing on my oxygen pipe (氧气管)!\ The patient’s suffering (痛苦) had something to do with ______.