问题：
[单选题]2008年奥运会上,光纤通信网将覆盖所有的奥运场馆,为各项比赛提供安全、可靠的通信服务,光纤通信是利用光的全反射将大量信息高速传输.若采用的光导纤维是由内芯和包层两层介质组成,下列说法正确的是()
A、内芯和包层折射率相同,折射率都大
B、内芯和包层折射率相同,折射率都小
C、内芯和包层折射率不同,包层折射率较大
D、内芯和包层折射率不同,包层折射率较小
参考答案：
B
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