【正确答案】正确答案：Morpheme is the smallest meaningful linguistic unit of language, not divisible or analyzable into smaller forms. What is usually considered a single word in English may be composed of one or more morphemes. Take disagreeable for example, it contains three morphemes, dis-, agree and -able. A morpheme may take various shapes or forms. For instance, -ion, -tion, -sion and -ation are the positional variants of the same suffix. They do not differ in meaning or function but show a slight difference in sound depending on the final phoneme of the preceding verb. They are called allomorphs. So an allomorph is any of the variant forms of a morpheme as conditioned by position or adjoining sounds.