people are riding motorcycles in a circle.
People are on motercycles
If you are riding a motorcycle, you are on it.
exists e1 x1 x2 x3.(in(e1,x3) & n_circle(x3) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_motorcycle(x2) & n_people(x1))
exists p1 x1.(exists x2.(on(x1,x2) & n_motercycle(x2)) & n_people(x1))