People are doing various activities on the beach.
People are walking on a beach.
Various activities might not include walking -- it could be swimming, sunbathing, running, etc.
exists e1 s1 x1 x2 x3.(n_beach(x3) & on(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_activity(x2) & a_various(s1) & Theme(s1,x2) & n_people(x1))
exists e1 x1 x2.(on(e1,x2) & n_beach(x2) & Actor(e1,x1) & v_walk(e1) & n_people(x1))