Final answer:
The Overwrite import type should be used to refresh a product catalog data extension that changes daily, as it updates the data extension with the most recent information and removes any obsolete products.The correct option is a.
Step-by-step explanation:
If a consultant has a data extension containing all current product information and the customer wishes to refresh the data each morning by importing a CSV file with today's product catalog, the import type that should be used is Overwrite. This is because the product catalog changes every day, with products being added or removed. Using the Overwrite import option ensures that the data extension will contain only the most recent data, reflecting the current state of the product catalog without keeping any outdated records. Using Add Only would not remove old products that are no longer available, while Update Only would not add new products. Add/Update could add new products and update existing ones but would also leave the old, removed products in the data extension.