Is the book wrong?

I was reading through the USCG-AUX Boating Skills and Seamanship book, and in the section on inland boating, one of the practice questions asks the following:

As you travel upstream, which bank is on your port side?

a. right
b. left
c. First National
d. left descending bank

The answer key shows the answer to be “d.”, but isn’t the correct answer the “right descending bank”?

left…because it is on your port/left side.
desending…because you are headed upstream

Still confused.

[b]RIVERBANK NAMES.[/B] The banks of rivers are referred to as “left” and “right” from the perspective of a vessel traveling downstream. Thus, the right bank has green ATONs and the left bank has red ATONs. The west bank of the Mississippi is its right bank and has green ATONs.

To avoid confusion, commercial traffic often calls the right bank the right descending bank and the left bank the left descending bank. Expressed in this way, it leaves no doubt in your mind.

What am I missing?

After googling-up some refresher, it looks like the correct answer is “a”.

That’s definitely the best of the options, but I still think the correct answer is right descending bank.

You quoted this earlier: “The banks of rivers are referred to as “left” and “right” from the perspective of a vessel traveling downstream” The “descending” is not necessary. “left” and “right” automatically assume you are descending. The “descending bank” wording is just to avoid confusion, it is not required in order to be correct.