You Have Been Given Two Tables,CUSTOMER and SALE

Multiple Choice

You have been given two tables,CUSTOMER and SALE.You want to check the referential integrity constraint: SALE.CustomerNumber must exist in CUSTOMER.CustomerNumber
You run the following SQL query:
SELECT CustomerNumber
FROM SALE
WHERE CustomerNumber NOT IN
(SELECT CustomerNumber
FROM CUSTOMER) ;
What is shown in the results of this query?

A) All values of CustomerNumber that match the constraint.
B) All values of CustomerNumber that violate the constraint.
C) All values of CustomerNumber where
SALE.CustomerNumber = CUSTOMER.CustomerNumber.
D) All values of Customer number that are in CUSTOMER but not in SALE.