Final answer:
The maximum number of themes that can be added to a Shopify store is 20. Shopify allows you to have multiple unpublished themes, but only one can be published at a time.
Step-by-step explanation:
The maximum number of themes that can be added to a Shopify store is 20 (option D).
Shopify allows you to add multiple themes to your store, but there is a limit to how many unpublished themes can be added. Once this limit is reached, you must remove a theme before adding a new one. However, only one theme can be published at a time.
For example, if you have 20 unpublished themes in your Shopify store and you want to add a new theme, you will need to remove one of the unpublished themes to make room for the new one. This ensures that your store only has one published theme at a time.