Answer:
A) an underextension error
Step-by-step explanation:
"Underextension occurs when a categorical term (a word used to describe a group of things) is used in language improperly by only using it for one object instead of all objects that belong in that category. This often occurs in children when they are initially acquiring and developing language. Children will frequently not apply a new word to objects that it should be applied to."
Reference: AlleyDog.com. “Underextension.” Underextension Definition | Psychology Glossary, 2019