Which Transact-SQL statement should you use?

You administer a Microsoft SQL Server 2012 database named Orders.
Orders contains a table named OrderShip that is defined as follows:

A NULL value represents a domestic order. Ninety percent of the values in CountryCode are NULL.
Customers require a procedure that will return orders for all customers from a specified country.
You create a new procedure:

Performance on this procedure is slow.
You need to alter the schema to optimize this query. Objects created must use a minimum amount of resources.
Which Transact-SQL statement should you use?

A.
CREATE NONCLUSTERED INDEX IX_CountryCode ON Ordership (CountryCode) WHERE CountryCode IS NOT NULL

B.
CREATE STATISTICS ST_CountryCode ON OrderShip (CountryCode) WHERE CountryCode IS NOT NULL

C.
CREATE CLUSTERED INDEX IX_CountryCode ON OrderShip (CountryCode)

D.
CREATE INDEX IX_CountryCode ON OrderShip (CustomerID) WHERE CountryCode IS NOT NULL