第21题:[单项选择]<br><br><br/>A.Thesadnessofbeinginvolvedinaccidents.<br/>B.Waystolimittheuseofprivatecars.<br/>C.Theseriouspollutiononmotorroads.<br/>D.Freedomtotravelquicklyandsafely.<br/>参考答案:B 答案解析:[听力原文] 29-31 The private motor vehicle has given us a freedom our ancestors could not dream a