The alphanumeric display shows only voltage and frequency when you select one of these pushbutton.
答案解析
解析：
### 题干解析
题干的意思是：“当你选择这些按钮中的其一时，数字字母显示只出现电压和频率。”这里有几个重要的关键词：
1. **选择按钮**：指的是用户可以操作的控制按钮。
2. **数字字母显示**：指的是显示屏的类型，通常是指数字显示（如LCD屏幕）而不是模拟显示（如指针式表盘）。
3. **电压和频率**：这是显示的内容，说明这个设备主要用于测量电压和频率。
### 选项分析
- **A. 当你选择这些按钮中的其一时，数字字母显示只出现电压和频率。**
- 这个选项直接对应了题干的描述，强调了“数字字母显示”这一点。
- **B. 当你选择这些按钮中的其一时，模拟数字显示只出现电压和频率。**
- 这个选项提到了“模拟数字显示”，但实际上“模拟”和“数字”是两种不同的显示方式，题干中明确提到的是“数字字母显示”，所以这个选项不正确。
- **C. 当你选择这些开关中的其一时，模拟数字显示只出现电压和频率。**
- 这个选项同样提到了“模拟数字显示”，而且使用了“开关”这个词，和题干中的“按钮”不一致，因此也不正确。
### 正确答案
因此，正确答案是 **A**，因为它准确地反映了题干的意思。
### 深入理解
为了帮助你更好地理解这个知识点，我们可以用一个生动的例子来说明。
想象一下你在一个实验室里，面前有一个多功能的测量仪器。这个仪器有很多按钮，每个按钮都可以选择不同的测量模式。比如说，有一个按钮可以让你测量电压，另一个按钮可以测量频率。当你按下其中一个按钮时，仪器的显示屏上会出现数字，比如“220V”表示电压，或者“50Hz”表示频率。
在这个例子中，显示屏就是“数字字母显示”，而你按下的按钮就是题干中提到的“这些按钮”。如果你选择了电压测量，显示屏上只会显示电压的数值，而不会显示其他信息，比如电流或功率。这就是题干所描述的情境。
### 总结
相关知识点：
按钮选其一显示啥要记牢
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