Two females ride camels backs.
Two females on camels.
females ride camels backs implies that they are on camels.
exists e1 x1 x2 x3.(Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_back(x2) & of(x2,x3) & n_camel(x3) & n_female(x1) & card_eq_2(x1))
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_camel(x2) & n_female(x1) & card_eq_2(x1))