fill data dynamically in a combo box in Userform

I'm still learning about VBA programming and I need to know how to fill data dynamically in a combo box when checking many checkpoints without a specific order.

Thank you so much for your help !

The image that I attached to this message describes the situation. Actually I would like to when checking for example the boxes "a" and "c" list in the comboboxes the list of data that refer to a and c.

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