Which ORDER BY clause are valid for the above query?

Evaluate the following SQL statement:
SQL> SELECT cust_id, cust_last_name “Last Name”
FROM customers
WHERE country_id = 10
UNION
SELECT cust_id CUST_NO, cust_last_name
FROM customers
WHERE country_id = 30;
Which ORDER BY clause are valid for the above query? (Choose all that apply.)

A.
ORDER BY 2, 1

B.
ORDER BY CUST_NO

C.
ORDER BY 2, cust_id

D.
ORDER BY “CUST_NO”

E.
ORDER BY “Last Name”

Explanation:
Using the ORDER BY Clause in Set Operations
– The ORDER BY clause can appear only once at the end of the compound query.
– Component queries cannot have individual ORDER BY clauses.
– The ORDER BY clause recognizes only the columns of the first SELECT query.
– By default, the first column of the first SELECT query is used to sort the output in an ascending order.