单选题 The study of characteristics of language varieties, the characteristics of their functions, and the characteristics of their speakers fall into the field of ______ as these three constantly interact and change with a speech community.
【正确答案】 B
【答案解析】解析：考查社会语言学。社会语言学研究语言的多样性、语言的功能特征和说话者的特征，以及这三者如何在言语社团中持续的交互作用和变化。