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问题 单项选择题

旋转阳极X线管与固定阳极管比，优点是

A．焦点大，功率小
B．焦点小，功率大
C．焦点大，功率大
D．焦点小，功率小
E．焦点功率均不变

答案

参考答案：B

解析：电子撞击的是靶面圆环面积，散热比固定阳极管快，因此焦点变小，功率变大。

改错题

短文改错。

     短文中共有10处错误，每句中最多有两处。错误涉及一个单词的增加﹑删除或修改。

     增加：在缺词处加一个漏词符号（∧），并在此符号下面写出该加的词。

     删除：把多余的词用（﹨）划掉。

     修改：在错的词下面划一横线，并在该词的下面写出修改后的词。

     注意：1. 每处错误及其修改均仅限一词； 

                2.只允许修改10处，多者（从第11处起）不计。

Dear friends,

      It is real a good chance to have met all of you here. We have spent several preciously weekends in learning

in the English Club. Although we have been members for a short period of times, we have made great progresses. That is because we are all very much active and the activities are not only enjoyable and also helpful. Besides,

the foreign teachers here working hard and try their best to make the activities lively and interested. I am very

pleased to say all of us greatly improved our spoken English so far. I am looking forward to see all of you again

in the near future!

___________________________________________________________________________________________
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单项选择题

再次免疫应答的主要抗体是（）

A.IgE

B.IgG

C.IgD

D.IgM

E.IgA
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