A. Drop the UDF and rewrite the report query as follows:
SELECT c.CustomerName
FROM Sales.Customer c
INNER JOIN Sales.Customer s ON c.CustomerID = c.CustomerID
GROUP BY c.CustomerID
HAVING MAX(s.OrderDate) < DATEADD(DAY, -90, GETDATE())

B. Drop the UDF and rewrite the report query as follows:
SELECT c.CustomerName
FROM Sales.Customer c
WHERE NOT EXISTS (
SELECT s.OrderDate
FROM Sales.SalesOrder s
WHERE s.OrderDate > DATEADD(DAY, -90, GETDATE())
AND s.CustomerID = c.CustomerID
)

C. Drop the UDF and rewrite the report query as follows:
SELECT DISTINCT c.CustomerName
FROM Sales.Customer c
INNER JOIN Sales.SalesOrder s ON c.CustomerID = s.CustomerID
WHERE s.OrderDate < DATEADD(DAY, -90, GETDATE())

D. Rewrite the report query as follows:
SELECT c.CustomerName
FROM Sales.Customer c
WHERE NOT EXISTS (
SELECT OrderDate
FROM Sales.ufnGetRecentOrders(c.CustomerID, 90)
)
Rewrite the UDF as follows:
CREATE FUNCTION Sales.ufnGetRecentOrders(@CustomerID int,
@MaxAge datetime)
RETURNS @OrderTable TABLE (OrderDate datetime) TABLE
AS
BEGIN
INSET @OrderTable
SELECT OrderDate
FROM Sales.SalesOrder s
WHERE s.CustomerID = @CustomerID
AND s.OrderDate > DATEADD(DAY, -@MaxAge, GETDATE())
RETURN
END