Which sentence does the subject agree with the verb? Those classes joins the team every year.
Mrs. Smith like her students to participate.
She encourage her entire class to sign up for an event.
They always win a ribbon for best student participation.

They always win a ribbon for best student participation.

The first one should be “those classes join the team every year” because if classes is plural then join is singular

The other two are the opposite of that. Mrs. Smith is one person so she likes (with an s) her students to participate and she encourages (also with an s) her entire class to sign up.