A large crowd standing in front of a busy building.
People are outside of a structure.
A large crowd means a set of people.  In front of a building means outside the building, hence the people are outside.
exists s1 s2 x1 x2 x3 x4.(a_topic(x1) & in(x1,x3) & of(x3,x4) & n_building(x4) & a_busy(s2) & Theme(s2,x4) & n_front(x3) & n_standing(x1) & of(x1,x2) & n_crowd(x2) & a_large(s1) & Theme(s1,x1))
exists e1 x1 x2.(of(e1,x2) & n_structure(x2) & r_outside(e1) & Actor(e1,x1) & v_be(e1) & n_people(x1))