关于优先编码器描述正确的是（）
A. 任何时刻只允许输入一个有效编码请求信号
B. 在优先编码器中，允许同时输入两个以上的有效编码请求信号。
C. 当几个输入信号同时出现时，只对其中优先权最低的一个进行编码。
目前经常使用的编码器有（ ）。
A. 普通编码器
B. 优先编码器
C. 16线—4线编码器
Listen to the short conversations and choose the best answer to each question you have heard.
A. a. They are guide and visitor.
B. b. They are husband and wife.
C. c. They know each other well.
D. d. They meet for the first time,
No. 16
A. a. It was noisy.
B. b. His baby was sick.
C. c. It was boring.
D. d. His watch went wrong.
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