The sentence that uses an action verb is "Wild horses galloped through the canyon."
An action verb expresses an action or activity performed by the subject of the sentence, in this case, the subject "wild horses" and the action verb "galloped"
The other three sentences "Pat has been on the soccer team for a year." "You will be 10 years old in June." "Was that math problem difficult?" have linking verbs, linking verbs indicate a state of being or condition of a subject, such as "has been", "will be", "was" respectively. They don't describe an action being performed.