Examine the SQL statements that creates ORDERS table: CREATE TABLE orders (SER_NO NUMBER UNIQUE, ORDER_ID NUMBER, ORDER_DATE DATE NOT NULL STATUS VARCHARD2(10) CHECK (status IN ('CREDIT','CASH')), PROD_ID_NUMBER REFERENCES PRODUCTS(PRODUCT_ID), ORD_TOTAL NUMBER, PRIMARY KEY (order id, order date)); For which columns would an index be automatically created when you execute the aboveSQL statement? （）

A. SER_NO
B. ORDER_ID
C. STATUS
D. PROD_ID
E. ORD_TOTAL
F. Composite index on ORDER_ID and ORDER_DATE