Which two statements are true about constraints? （）

A.You can join a maximum of two tables through an equijoin.
B.You can join a maximum of two columns through an equijoin.
C.You specify an equijoin condition in the SELECT or FROM clauses of a SELECT statement.
D.To join two tables through an equijoin, the columns in the join condition must be primary key and foreign key columns.
E.You can join n tables (all having single column primary keys) in a SQL statement by specifying a minimum of n-1 join conditions.

A.SELECT e.last_name, d.department_id, d.department_name, l.city FROM departments d RIGHT OUTER JOIN employees e ON d.department_id = e.department_id RIGHT OUTER JOIN locations l ON d.location_id = l.location_id;
B.SELECT e.last_name, d.department_id, d.department_name, l.city FROM departments d FULL OUTER JOIN employees e ON d.department_id = e.department_id FULL OUTER JOIN locations l ON d.location_id = l.location_id;
C.SELECT e.last_name, d.department_id, d.department_name, l.city FROM departments d LEFT OUTER JOIN employees e ON d.department_id = e.department_id LEFT OUTER JOIN locations l ON d.location_id = l.location_id;
D.SELECT last_name, department_id, department_name, city FROM departments d NATURAL JOIN employees e NATURAL JOIN locations l;

A.creates a view with constraints
B.creates a view even if the underlying parent table has constraints
C.creates a view in another schema even if you don't have privileges
D.creates a view regardless of whether or not the base tables exist