请教几个OCP-007的3个问题，望高手解答

1 select e.employee_id,e.last_name,e.department_id,d.department_name from employees e,department d
  where e.department_id=d.department_id
in the statement,which capabilities of SELECT statement are performed?
  A. selection,projection,join
  B. difference,projection,join
  C. selection,intersection,join
  D. intersection,projection,join
  E. difference,projection,join
2 which view should a user query to display the columns associated with the constraints on a table 
  owned by the user?
  
  A.USER_CONSTRAINTS
  B.USER_OBJECTS
  C.ALL_CONSTRAINTS
  D.USER_CONS_COLUMNS
  E.USER_COLUMNS
请问这两题应该怎么理解题目的意思？