对220kV系统，线路后备保护的配置原则是：

A．宜采用断路器失灵保护做后备方式;

B．宜采用远、近结合的后备方式;

C．宜采用远后备方式;

D．宜采用近后备方式;但某些线路如能实现远后备，则宜采用远后备方式，或同时采用远、近结合的后备方式。

She was grateful _____ George _____ all _____he had done.

A．to; for; that

B．to; for; what

C．for; to; that

D．for; to; what