Final answer:
Mary must ensure that the product detail page includes all mandatory attributes to qualify for the Featured Offer (option C). These attributes typically encompass a comprehensive description, images, and specifications.
Step-by-step explanation:
Mary, a vendor who wants to make sure their product listing is eligible for the Featured Offer, has rightly checked stock availability, compliance documents, and pricing. The last required criterion she needs to check to ensure eligibility for the Featured Offer is that mandatory attributes are present on the product detail page.
These mandatory attributes usually include detailed product descriptions, images, specifications, and any other information that would aid a customer in making an informed purchasing decision. By ensuring that these elements are accurate and comprehensive, Mary can increase her chances of her product being selected as the Featured Offer.