How to add keyboard(vk api) to variable?

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Good evening, Khabrovtsy. Interested in the question. How to add a keyboard call function to a variable?
In general, maybe you can help me with the best option: I want to make tests in the VK group, for this I want to do the following:
1) Create a variable
2) Assign a keyboard call to this variable
3) I want to use this variable in responses.
When creating a simple keyboard without variables, I got the following problem: At the beginning of the test, you could enter the last answer and the answer immediately comes "you have successfully passed the test"