应该是b,这是个定语从句,应该听说过吧,
The basic features of the communication process are expressed in one question,who says ___through what channel to whom.
A what B when C such D how
此句中后半句的who是代前半句的one question,而这个question又是叙述交流程序的基本特点的,所以后半句主要做个概述怎样说,
when through what channel to whom,本句中的whom就是指一个人的宾格,凡以后就是,什么时候和什么人说什么,这个channel 就是内容的意思.