Two younger people are being pulled on watercraft behind a boat.
Two teenagers are tubing on a lake.
Younger people may or may not be teenagers.   Tubing is not the only activity two young people may be pulled behind a boat.
exists e1 s1 x1 x2 x3.(behind(e1,x3) & n_boat(x3) & on(e1,x2) & n_watercraft(x2) & Theme(e1,x1) & v_pull(e1) & n_people(x1) & r_more(s1) & a_younger(s1) & Theme(s1,x1) & card_eq_2(x1))
exists e1 x1 x2.(on(e1,x2) & n_lake(x2) & Actor(e1,x1) & v_tube(e1) & n_teenager(x1) & card_eq_2(x1))