The teenage boy is grinding a skateboard on a steep rail.
A teenager does a trick on a skateboard.
Grinding is a type of trick done on a skateboard.
exists e1 s1 x1 x2 x3 x4.(n_boy(x1) & of(x1,x2) & n_teenage(x2) & Theme(e1,x3) & Actor(e1,x1) & v_grind(e1) & on(x3,x4) & n_rail(x4) & a_steep(s1) & Theme(s1,x4) & n_skateboard(x3))
exists e1 x1 x2 x3.(on(e1,x3) & n_skateboard(x3) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_trick(x2) & n_teenager(x1))