Which two CREATE INDEX statements are valid?

View the Exhibit and examine the structure of ORD and ORD_ITEMS tables.

The ORD_NO column is PRIMARY KEY in the ORD table and the ORD_NO and ITEM_NO
columns are composite PRIMARY KEY in the ORD_ITEMS table.
Which two CREATE INDEX statements are valid? (Choose two.)

A.
CREATE INDEX ord_idx1
ON ord(ord_no);

B.
CREATE INDEX ord_idx2
ON ord_items(ord_no);

C.
CREATE INDEX ord_idx3
ON ord_items(item_no);

D.
CREATE INDEX ord_idx4
ON ord,ord_items(ord_no, ord_date,qty);

Explanation:
How Are Indexes Created?
You can create two types of indexes.
Unique index:The Oracle server automatically creates this index when you define a column in a
table to have a PRIMARY KEY or a UNIQUE constraint. The name of the index is the name that is
given to the constraint.
Nonunique index:This is an index that a user can create. For example, you can create the
FOREIGN KEY column index for a join in a query to improve the speed of retrieval.
Note:You can manually create a unique index, but it is recommended that you create a unique
constraint, which implicitly creates a unique index.