The ballerina dancer stands on her toes with outstretched arms.
couples dances on a song
A ballerina refers to one woman.  Whereas, couples indicate more than one person.
exists e1 s1 x1 x2 x3 x4.(n_toe(x3) & of(x3,x1) & n_female(x1) & n_dancer(x1) & of(x1,x2) & n_ballerina(x2) & with(e1,x4) & n_arm(x4) & a_outstretched(s1) & Theme(s1,x4) & on(e1,x3) & Actor(e1,x1) & v_stand(e1))
exists x1 x2 x3.(a_topic(x1) & on(x1,x3) & n_song(x3) & n_dance(x1) & of(x1,x2) & n_couple(x2))