Which Transact-SQL statement should you use?

You are a database developer of a Microsoft SQL Server 2012 database.
The database contains a table named Customers that has the following definition:

You need to ensure that the CustomerId column in the Orders table contains only values that exist in
the CustomerId column of the Customer table.
Which Transact-SQL statement should you use?

A.
ALTER TABLE Orders
ADD CONSTRAINT FX_Orders_CustomerID FOREIGN KEY (CustomerId) REFERENCES
Customer (CustomerId)

B.
ALTER TABLE Customer
ADD CONSTRAINT FK_Customer_CustomerID FOREIGN KEY {CustomerID) REFERENCES
Orders (CustomerId)

C.
ALTER TABLE Orders
ADD CONSTRAINT CK_Crders_CustomerID
CHECK (CustomerId IN (SELECT CustomerId FROM Customer))

D.
ALTER TABLE Customer
ADD OrderId INT NOT NULL;
ALTER TABLE Customer
ADD CONSTRAINT FK_Customer_OrderID FOREIGN KEY (CrderlD) REFERENCES Orders
(CrderlD);

E.
ALTER TABLE Orders
ADD CONSTRAINT PK Orders CustomerId PRIMARY KEY (CustomerID)

Explanation:
http://msdn.microsoft.com/en-us/library/ms189049.aspx