You can make a CAPTCHA plugin, see plugin docs here and captcha section here.
I'm sure somebody made a CAPTCHA plugin that allowed you to write pre-determined questions, which would suit your case very well. But I cannot find it now.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask in English.
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July 15, 2020: Q2A 1.8.5 released!