Answer:
subject-verb agreement is when the subject and the verb must agree with each other in number (singular or plural). so if a subject is singular the verb must also be singular and vice versa.
Step-by-step explanation:
if the subject is singular (dog) add an "s" to the verb (walks)
but if the subject is plural (dogs) don't add an "s" to the verb (walk)
example : the dog walks down the street / the dogs walk down the street