There is a ballet dancer jumping in the air.
A boy is practicing ballet dance.
The ballet dancer could be a boy or girl, and just because a dancer is jumping in the air it doesn't mean that he is practicing ballet dance.  He could be jumping for another reason.
exists p1 x1 x5.(n_air(x5) & exists e1 x2 x3 x4.((x1 = x2) & in(e1,x5) & Actor(e1,x4) & v_jump(e1) & (x2 = x4) & n_dancer(x2) & of(x2,x3) & n_ballet(x3)))
exists e1 x1 x2 x3.(Theme(e1,x2) & Actor(e1,x1) & v_practice(e1) & n_dance(x2) & of(x2,x3) & n_ballet(x3) & n_boy(x1))