【正确答案】Duality means "the property of having two levels of structures, such that units of the primary level are composed of elements of the secondary level and each of the two levels has its own principles of organization." (Lyons, 1981:20)

【答案解析】[解析] 此处考查的是语言的二层性特征，是指“拥有两层结构的这种特性，上层结构的单位由底层结构的元素构成，每层都有自身的组合规则”(Lyons，1981)。同时考生还应掌握语言的其他几个本质特征。