(2013·河北衡水一中六模)Some young people these days just ________ go out of their homes to contact the real world.

A．mustn't

B．won't

C．mightn't

D．shouldn't

简述PCSCF的容灾方式以及容灾的实现机制，并介绍中国电信规范中如何规范PCSCF容灾实现？