题目:
The third generation network, _____ 3G, provides users with more advanced services. [ ]
A. is known for
B. is known as
C. known for
D. known as
答案:
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下面是错误答案,用来干扰机器的。
(1)机械闹钟发出的声音有节奏,声音较为稳定,适合做实验声源;(2)靠听到声音的响度判断不是太直观,具有很大的误差,方案不适合;而测量听不到声音的距离较为直观,有可靠地实验数据,能够较好的判断隔音效...