The statement "They are used to show agreement." is true regarding agreement verbs. Agreement verbs indicate the agreement between the subject and the verb, often reflecting characteristics such as number, person, or gender.
The other options provided are incorrect or misleading:
- Agreement verbs typically don't identify the subject and object of the verb; they indicate agreement in some grammatical feature.
- Agreement verbs can be used in negative sentences.
- The requirement for a classifier to precede the verb is not a general rule applicable to all languages; it varies by language context.
Thus, the first statement is the most accurate.