X线管的正确使用步骤是（）
A.检查冷却装置，灯丝加热，逐步加高压
B.检查冷却装置，灯丝加热，逐步减高压
C.检查滤过板装置，限时器，电源开关
D.检查电源，kV和mA指示表盘及调节旋钮
E.检查机头的各种滤过板显示装置
参考答案：A
解析：在使用设备前，先检查冷却装置。在使用时应先将其灯丝加热至所需要的温度，然后再加高压，产生X线。X线球管产热很多，使用中应特别注意每天开机前或停机时间较长时，要由低mA，低kV上升。此外还应避免X线管的超负荷使用。
The bell for class rang. All the students took out their 1 , waiting for the teacher. Our Chinese teacher, Miss Liu, had told us before that we were going to write a composition 2 class. A minute passed, and another, 3 the teacher didn't appear. We began to wonder what the matter with her was. Was she ill? Or had she forgotten about the class? 4 could tell. Soon some students began to study other subjects, some students began to talk and even made 5 . About ten minutes later, the door opened and Miss Liu 6 came in, smiling. She didn't say sorry to the class. We felt 7 angry. The teacher often told us never to be late for class and said it was 8 manners to be late. She also said that if we were late, we should make an apology (道歉) 9 at once or after class. But now she was late and had kept the whole class waiting for such a long time and didn't even tell us the reason. It was unfair. At this moment, Miss Liu picked up a piece of chalk(粉笔) and 10 "Teacher IsLate" on the blackboard and said that was the topic of our composition today. All of us smiled and understood what the teacher meant.
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