You obviously don't understand the problem. Just to make it clear: I was doing the listening exercise. And as far as I understand it, you can either say "ett øyeblikk" ("one eye glance") or "et øyeblikk" ("an eye glance").
I got a nice explanation to the Norwegian "a" and "one" in another discussion from the user fveldig (who seems to be a native speaker) that I want to share:
feminine: ei masculine: en neuter: et
feminine: éi(/ei) masculine: én(/en) neuter: ett
"one, two three" is usually "én(/en), to, tre", although in some regions you'd say "ett, to, tre", but this is less common.
So the translation of "Just a moment" would have to be "Et øyeblikk!" while the listening exercise would have to accept "Et..." as well as "Ett...".
Listening exercises only accepts the spelling of the preferred translation, so only 'et øyeblikk' is accepted. The only options are to either disabling the listening exercise, or keep it as it is.
Given that 'et øyeblikk' is 50 times more common than 'ett øyeblikk', and that it is a relatively common expression, it seems reasonable to keep it as it is.