问题
单项选择题
旋转阳极X线管不具备下列哪一特点（）
A.结构复杂造价较高
B.功率大
C.有效焦点面积小
D.传导散热能力强
E.热量分散到整个靶面上
答案
参考答案：D
解析：旋转阳极X线管热量分散到整个靶面上，所以功率大，焦点面积小；但靶盘的热量主要是通过靶盘的热辐射散发出去，被管外的绝缘油吸收，所以散热较慢。
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旋转阳极X线管不具备下列哪一特点（）
A.结构复杂造价较高
B.功率大
C.有效焦点面积小
D.传导散热能力强
E.热量分散到整个靶面上
参考答案：D
解析：旋转阳极X线管热量分散到整个靶面上，所以功率大，焦点面积小；但靶盘的热量主要是通过靶盘的热辐射散发出去，被管外的绝缘油吸收，所以散热较慢。
Escaping a fire is a serious matter. If you know what to do during a fire, you can __1__ a life. It is important to know the ways you can use and __2__ them to everyone in the family, such as stairs and fire escapes(安全出口). You shouldn’t take lifts. From the lower floors of the building, escape __3__ windows is possible. Let’s learn the best way of leaving by window with the least chance of serious injury(受伤). The first floor window is usually not very high from the ___4____ . It is about the height of a man. Of course, it is safer to jump a short way than stay in a burning building. Windows are also very useful when you are___5___ for help. Be sure to keep the door ___6__ before opening the window. If we don’t do that, ___7__and fire may come into the room. Keep your head low at the window to be sure you get__8__ fresh air instead of smoke. On the second or third floor, the best windows for escape are those __9____open onto a roof. From the roof a person can drop to the ground more __10____ .Dropping onto the cement(水泥地) might end in injury. Trees and grass can help to break a fall.
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