question: Which actor did M1 , M2 , and M3 employ
query: SELECT DISTINCT ?x0 WHERE {
  ?x0 a ns:film.actor .
  ?x0 ns:people.person.employment_history/ns:business.employment_tenure.company M1 .
  ?x0 ns:people.person.employment_history/ns:business.employment_tenure.company M2 .
  ?x0 ns:people.person.employment_history/ns:business.employment_tenure.company M3
  }