题干

关于原子核的衰变下列说法正确的是(   )

A:对于一个特定的衰变原子,我们只知道它发生衰变的概率,而不知道它将何时发生衰变

B:放射性元素A经过2次α衰变和1次β衰变后生成一新元素B,则元素B在元素周期表中的位置较元素A的位置向前移动了2位

C:β衰变的实质在于核内的质子转化成了一个中子和一个电子

D:碘131的半衰期约为8天,若某药物含有质量为m的碘131,经过32天后,该药物中碘131的含量大约还有 m16

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答案(点此获取答案解析)

A,C

同类题3

       My now 7-year-old grandson, who lives 100 miles away, has kept my phone number in his mind since he was 4. Since then, he has been  1 me every night before he goes to bed to tell me about his day or just to say “Good night, Grandma.”
    He also often calls me at other times during the day just to  2  a happy or sad moment. Many times he's playing a basketball with one hand, or laughing with a friend about something that I  3quite understand, or crying about something he may or may not want to talk about while I'm on the other end of the phone. I just listen and empathize (同情) or laugh with him—just share his current (当前的)  4 . I always let him control the  5  , and the time he's on the phone with me. Many times I just listen to him play, or play games we've made up together that we can play over the  6 .   
      The only time I take control of the 7  is when he's ready to say goodbye at night. Often there are four special   8  I say to him every night. One night I thought maybe he was tired to hear those, so I didn't say them. He  9 called me back and told me that I forgot to say those sentences! I haven’t missed saying them since then!
      My friends all know that he is the most important for me.  10  I'm in church(教堂), or some place where I really can't take his call, I always politely excuse myself and talk to him, even if it's just for a minute to tell him I'll call him back in a few minutes.
He knows that he takes first place in my heart.