A person is riding his dirt bike.
A man rides his dirt bike on a track course.
Dirt bikes can be ridden off road, it doesn't have to be a track course.
exists e1 x1 x2 x3.(Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_bike(x2) & of(x2,x3) & n_dirt(x3) & of(x2,x1) & n_male(x1) & n_person(x1))
exists e1 x1 x2 x3 x4 x5.(on(e1,x4) & n_course(x4) & of(x4,x5) & n_track(x5) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_bike(x2) & of(x2,x3) & n_dirt(x3) & of(x2,x1) & n_male(x1) & n_man(x1))