His business prospered and he became a person of means. Yet, despite his great riches, he gave no arms to the needy and no thanks to his benefactors whose savings ______ to his welfare.

A．had contributed.

B．contributed

C．were contributed

D．did contribute

光纤传光是通过光的什么特性来实现的（）

A、直线传播

B、折射

C、反射

D、全反射