Physically challenged person sitting on his wheelchair in a park.
A young couple sits on a bench in the park.
A person is singular, a couple are two people.  A wheelchair is not a bench.
exists e1 e2 x1 x2 x3 x4.(a_topic(x1) & in(e2,x4) & n_park(x4) & on(e2,x3) & n_wheelchair(x3) & of(x3,x1) & n_male(x1) & Actor(e2,x2) & v_sit(e2) & (x1 = x2) & n_person(x1) & Theme(e1,x1) & v_challenge(e1) & r_physically(x1))
exists e1 s1 x1 x2 x3.(n_park(x3) & in(e1,x3) & on(e1,x2) & n_bench(x2) & Actor(e1,x1) & v_sit(e1) & n_couple(x1) & a_young(s1) & Theme(s1,x1))