教师解析：

I. Morphology

The total number of words stored in the brain is called the lexicon. Words are the smallest free units of language that unite sounds with meaning.

Morphology is defined as the study of the internal structure and the formation of words.

II. Morphology and Morphemes

 The smallest meaningful unit of language is called a morpheme. •

 A morpheme may be represented by different forms, called allomorphs.

 It is a unit of form and meaning, a sign. The part of the morpheme we have referred to as its “form” is also called morph. A morph is a particular phonological form of a morpheme.•

 “zero” form of a morpheme and suppletives 

  • Some countable nouns do not change form to express plurality. Similarly, some regular verbs do not change form to indicate past tense. In these two cases, the noun or verb contains two morphemes, among which there is one “zero form” of a morpheme. 

  • Some verbs have irregular changes when they are in past tense. In this case, the verbs also have two morphemes. Words which are not related in form to indicate grammatical contrast with their roots are called suppletives.