What are synchronic and diachronic studies of language?请用英语回

The description of a language at some point of time (as if it stopped developing) is a synchrony study. The description of a language as it changes through time is a diachronic study. An essay entitled “On the Use of THE”, for example, may be synchronic, if the author does not recall the past of THE, and it may also be diachronic if he claims to cover a large range or period of time wherein THE has undergone tremendous alteration