[cardcounter0]

I think check/call is correct with unimproved ace, IF YOU KNOW YOU ARE UP AGAINST ANOTHER ACE. But how do you know this?

The answer is "it depends". Would the other player passively just call if his ace/kicker did hit instead of raising? Would the other player put you on two overs and call down with second pair? (and might bet the river if you check your ace?)

So it depends on what kind of hands the other player has shown and they have played them.

Absent reads, and being reasonably sure you are up against another ACE, check/call the river is the safe route.