A group of boys are playing on a beach.
The boy threw a ball.
Just because, a group of boys are playing on a beach does not imply that the boys threw a ball.
exists e1 x1 x2 x3.(on(e1,x3) & n_beach(x3) & Actor(e1,x1) & v_play(e1) & of(x1,x2) & n_boy(x2) & n_group(x1))
exists e1 x1 x2.(n_boy(x1) & Theme(e1,x2) & Actor(e1,x1) & v_throw(e1) & n_ball(x2))