求语言学morpheme and phoneme ,allophone,allomorph 的正确定义

Morpheme is the s smallest unit in term of expression and content,it is can not be further divided into smaller unit without destorying its meaning or dramatically altering the meaning .
Phoneme is the smallest uint of phonology.
Allophone is the variant of phones,they must bear some phonetic resemblelance.

(1)Morpheme is the smallest meaningful unit of a language.
(2)Phoneme is the abstract element of a sound, identified as being distinctive in a particular language.
(3)Allophone is the phonetic form in which a phoneme is realized.
(4)Allomorph is the phonetic form in which a morpheme is realized.