P （）refers to the realization of langue in actual use.

Social changes can often bring about language changes.

A diachronic study of language is the description of language at some point in time.

Phonology

Pragmatics

Findings in linguistic studies can often be applied to the settlement of some practical problems. The study of such applications is generally known as a（）linguistics.

Morphology

Phonetics

D（）is one of the design features of human language which refers to the phenomenon that language consists of two levels: a lower level of meaningless individual sounds and a higher level of meaningful units.

Language is p（）in that it makes possible the construction and interpretation of new signals by its users. In other words, they can produce and understand an infinitely large number of sentences which they have never heard before.