I'm sure there's an easier way to do it with scripting, but what you could do with the basic editor is:
You need as many pages as there are letters in the answer. They should all look the same.
Each page has links for A-Z.
Only the link for the correct letter goes to the page of the next letter in the answer. All the other links go back to the first page of entering the answer.
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If you have the advanced editor, you could set it up the same way, but:
Set up a variable X
Have all letters link to the next page, but only the correct choice also increases X by one.
When you get to the end, the options are "you got it wrong" and "you got it right."
"You got it right" is either grayed out or invisible unless X=(whatever the number of letters in the correct answer is)