A couple smiling while sitting.
the couple was sitting
was sitting is a rephrasing of smiling while sitting.
exists e1 e2 x1 x2.(a_topic(x1) & while(e1,e2) & Actor(e2,x2) & v_sit(e2) & Actor(e1,x2) & v_smile(e1) & (x1 = x2) & n_couple(x1))
exists e1 x1.(n_couple(x1) & Actor(e1,x1) & v_sit(e1))