第21题: [单项选择]PCM30/32系统的数码率是() A. 64kbit/s B. 8kbit/s C. 2048kbit/s D. 155.520Mbit/s 参考答案:C
第22题:[单选题]11 Air pollution has become _____ than ever before.We must do something to stop it. A.serious B.more serious C.most serious D.the most serious 参考答案:B