Adults ride a gondola on a sunny day.
adult singing on boat
Adults means more than one adult and adult is only one adult. Adults is not the same as adult. Just because there is an adult or adults that ride a gondola, it doesn't necessarily mean that the adult is singing.
exists e1 s1 x1 x2 x3.(on(e1,x3) & n_day(x3) & a_sunny(s1) & Theme(s1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_gondola(x2) & n_adult(x1))
exists x1 x2 x3.(a_topic(x1) & on(x1,x3) & n_boat(x3) & n_singing(x1) & of(x1,x2) & n_adult(x2))