单选题 (　　)is the study of the characteristics of language varieties, the characteristics of their functions and the characteristics of their speakers as these three constantly interact and change within a speech community.
【正确答案】 B
【答案解析】Sociolinguistics(社会语言学)包括语言的社会功能和语言使用者的社会特征，它研究语言变体的特征、它们的功能特征、讲话者的特征以及这三者如何在言语团体中持续地相互作用和变化。A为心理语言学，C为人类语言学，D为计算机语言学。