Answer: (a)

Explanation:
In a Dropshipping, the seller does not maintain inventory. Instead, when a customer places an order, the seller passes the order and shipping details to a third-party supplier or manufacturer, who then ships the product directly to the customer.

Key feature matching the question:
Seller controls pricing and marketing
No physical inventory held by seller
Fulfilment and shipping handled by third-party supplier

Other options are incorrect:
Affiliate model: earns commission by referring customers, no sales handling
Transaction fee model: charges fee per transaction (platform-based)
Agency model: acts as intermediary but does not necessarily involve direct supplier shipment like dropshipping.