ORDERS Name Null?

View the exhibit and examine the ORDERS table.
ORDERS
Name Null? Type
ORDER ID NOT NULL NUMBER(4)
ORDATE DATE DATE
CUSTOMER ID NUMBER(3)
ORDER TOTAL NUMBER(7,2)
The ORDERS table contains data and all orders have been assigned a customer ID. Which statement would add
a NOT NULL constraint to the CUSTOMER_ID column?

A.
ALTER TABLE orders
MODIFY CONSTRAINT orders_cust_id_nn NOT NULL (customer_id);

B.
ALTER TABLE orders
ADD CONSTRAINT orders_cust_id_nn NOT NULL (customer_id);

C.
ALTER TABLE orders
MODIFY customer_id CONSTRAINT orders_cust_nn NOT NULL (customer_id);

D.
ALTER TABLE orders
ADD customer_id NUMBER(6)CONSTRAINT orders_cust_id_nn NOT NULL;