Yes, B is the best of the choices. Choice A may not be 100% incorrect but looking at it more closely… In order to find out if no duplicate shipments happened, you'd need to trace shipping docs back to the invoices/sales records. Shipping documents that can't be tied to invoices of course means duplicate shipments or shipments for things not ordered. Assuming all of the shipped items were ordered, perhaps not all the quantity ordered was shipped initially, and a second shipment to complete the order was done later. (Choice B).
Tracing shipping documents to pre-numbered sales invoices won't tell you if duplicate billings occurred.
If a customer was indeed billed twice for an order, you'd probably look at the purchase order and verify quantity ordered, and compare it with quantity invoiced. If the numbers are different, it means that not everything ordered was shipped. If for some reason, the entire order wasn't filled (i.e., they ordered 20 units and you only sent 10 originally and then sent the other 10 later), you'd again look at purchase order and then the quantity invoiced. If they were invoiced twice for 20 units on the same purchase order, the error can easily be uncovered too – you'd have two invoices with two different invoice numbers. If they invoiced for the remaining 10 units later (correctly, but with a separate invoice) then all is good.
There's also a trick to use for questions like this… notice how the first words of the question are ‘shipping documents'. Chances are high that if one of the answer choices has similar words (in this case, ‘shipments'), it's probably going to be a candidate for a correct answer. Somebody pointed that out to me awhile back.
These assertion questions can be tough! I hope my response here makes sense. It's actually helpful for me because it helps me learn more as well. I took AUD this past week, and actually don't think I did that well on it. But, there is a centuries-old saying, “You don't understand a subject fully until you can teach it to someone else.”
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