Define the following term,giving examples for illustration:Allophone

Define the following term,giving examples for illustration:
Allophone

给出下面术语的定义,并举例说明:Allophone
Allophone:any of the different forms of a phoneme(eg.is an allophone of /t/in English.When /t/occurs in words like step,it is unaspirated.Bothand are allophones of the phoneme

给出下面短语的定义,并举例说明之:Allophone

给出下面词语的定义，并举例说明
音位变体/音素