光纤是利用光的折射原理工作的，光纤由纤芯和包层构成，且纤芯的折射率小于包层的折射率。

单项选择题The architecture of the Yuan Dynasty boldly increase the use of wooden frame structure, and the architectural characteristics of this time were extensive and uninhibited. Because the Mongolians love white, the Yuan Dynasty buildings mostly use white glazed tiles.( )

单项选择题What is the Chinese meaning of authoritative theory ? A、（媒介）规范理论 B、集权主义理论 C、自由主义理论 D、守门人理论