Hi @jmerriam ...
This is a common issue I come across when I am building quizzes for our instructors using the old/classic Quizzes interface. My solution does not involve letter choices at all. Instead, I do something like this:
1. What does 4 equal?
Sometimes, the answers inside the quotations are longer, but that's okay. I've not gotten any feedback from our instructors that this isn't working for students...so I'm assuming they are figuring things out as they take quizzes/tests/exams in Canvas.
Would something like this work for your needs?