, and the problem will be worked out.

A．If you have a bit more effort

B．Having a little effort

C．A bit more effort

D．There being a little effort

光纤通信限制中继距离的主要因素是（）。

A.数值孔径和模场直径

B.纤芯直径和包层直径

C.衰减和色散

D.纤芯不圆度和包层不圆度