第9题: [单项选择]The returning echoes the receiver picks up are ________. A. clearly audible bleeps B. inaudible to human ears C. immediately passed on to headphones D. filtered through the transmitter 参考答案:B 答案解析:[参考译文] 接收器收到的回声是——。
[试题分析] 本题是语义推理题。
[详细解答] 可从第四段第二句话分析出,回声超过人耳接收范围,听不到,先要filtered through circuit