Astudent who says "i saw the mouses run out of the whole" is having difficulty with what component of language?

A student who says "I saw the mouses run out of the whole" is having difficulty with PHONOLOGY, a component of language.

Phonology is defined as the study of the sound structure of language. Its basic unit is called phoneme, the smallest unit of sound that may cause a change of meaning within a language.

In the above sentence, instead of using the word "hole", a student erroneously uttered "whole". These two term sound the same but are of different meaning. 

("age" 51) i think this is it