I need a little help

I have a question which is not very relevent with CFA but i’m sure you (english natives) can help me. I have no friend whose english is mother language.

My friend and me, we discussed about the good pronunciation of the letter “s” in plurial words, for example “assumptions”, “politicians”, “nations”,…

i think the “s” in the three examples must be pronunced as /z/ as in “words”, “calls”, “bags”,… Because the 3 words are terminated by letter “n”.

But my friend said the letter “s” must be pronunced as /s/ as in “steps”, “books”, “hats”,… He argued that the ending letter “n” is never pronunced, that’s why my rule is not aplicable.

He and me, who is right?

many thanks.

You are.

Thank you very much!