People picking up trash in the park.
Some people are picking up trash to conserve the environment.
Some people indicates a limited number of people whereas "people" could an infinite number. Just because people are picking up trash doesn't mean they are doing it to conserve the environment.
exists e1 s1 x1 x2 x3 x4.(n_park(x4) & a_topic(x1) & in(e1,x4) & a_up(s1) & Manner(e1,s1) & Theme(e1,x3) & Actor(e1,x2) & v_pick(e1) & n_trash(x3) & (x1 = x2) & n_people(x1))
exists e1 p1 s1 x1 x2 x3 x4.(n_environment(x4) & Topic(e1,p1) & exists e2.(Theme(e2,x4) & Actor(e2,x1) & v_conserve(e2)) & a_up(s1) & Manner(e1,s1) & Theme(e1,x3) & Actor(e1,x2) & v_pick(e1) & n_trash(x3) & n_people(x2) & n_people(x1))