Correct Answer:
c.
SELECT InvoiceNumber, VendorName
FROM Invoices JOIN Vendors ON Invoices.VendorID = Vendors.VendorID
WHERE InvoiceTotal IN (SELECT MAX(InvoiceTotal) FROM Invoices)
Explanation:
All options only differ on the WHERE clause:
a: WHERE InvoiceTotal = MAX(InvoiceTotal)
Fails because aggregate functions (like MAX, COUNT, etc) have to be used on the SELECT clause.
b: WHERE InvoiceTotal = (SELECT MAX(InvoiceTotal))
Fails because the SELECT clause is incomplete.
c: WHERE InvoiceTotal IN (SELECT MAX(InvoiceTotal) FROM Invoices)
This one is correct, and returns the InvoiceNumber and VendorName register with the largest value on the InvoiceTotal field.