The Decision in the Case of Pharmaceutical Society of Great

The decision in the case of Pharmaceutical Society of Great Britain v Boots Cash Chemist (Southern) Limited [1953] 1 QB 401 means that when a customer shops at a supermarket,the offer is accepted and the contract is formed:

A) as soon as the customer enters the supermarket.
B) at the checkout,when the customer accepts the supermarket's offer to sell the goods.
C) when the customer accepts the goods on offer on the shelves by placing them in their basket.
D) at the checkout,when the supermarket accepts the customer's offer to buy the goods.