View the Exhibit and examine the structure of the EMP table. You executed the following command to add a primary key to the EMP table： ALTER TABLE emp ADD CONSTRAINT emp_id_pk PRIMARY KEY （emp_id） USING INDEX emp_id_idx； Which statement is true regarding the effect of the command？（）
- A The PRIMARY KEY is created along with a new index.
- B The PRIMARY KEY is created and it would use an existing unique index.
- C The PRIMARY KEY would be created in a disabled state because it is using an existing index.
- D The statement produces an error because the USING clause is permitted only in the CREATE TABLE command.