What's the purpose of product groups in a Shopping campaign?

Product groups allow you to organize and bid on specific subsets of your product inventory within a Shopping campaign. Instead of bidding on individual products, you use product groups to define which products from your Merchant Center feed are eligible to show for your ads. This enables granular control over your bidding strategy and ad spend, as you can set different bids for different product groups based on their performance or importance. The other options are incorrect because product groups are not predefined themes, keywords, or remarketing lists; they are a structural element for managing your product feed within a campaign.