X线管靶面上电子轰击的面积称
A．小焦点
B．大焦点
C．双焦点
D．有效焦点
E．实际焦点
参考答案：E
解析：电子聚焦后的实际撞击面积为实际焦点。
七成=7%．______．（判断对错）
— He tried to ____ how he felt but he failed.
— He is a person of few words but he is kind. [ ]
A. convey
B. survey
C. construct
D. study
