Which of the following accounts has a normal credit balance?
a. Sales Returns & Allowances
b. Sales
c. Merchandise Inventory
d. Delivery Expense

My guess would be b. Sales
But I'm not sure.

A is a Contra Revenue Account. Has a normal Debit Balance

B is a Revenue Account. Has a normal Credit Balance

C is a Current Asset Account. Has a normal Debit Balance

D is an Expense Account. Has a normal Debit Balance