None of the underwater workers has been harmed by the great fish. ________, most fish were so friendly that they played with the instruments.

A．Instead

B．Even though

C．However

D．Though

光纤特性测量项目包括哪些（）

A.中继段光纤线路损耗测量

B.中继段光纤后向散射信号曲线检测

C.测试光纤纤序的准确性

D.长途光缆链路偏振模色散（PMD）测量