When a Product Is Bought from the Supermarket, the Contract

When a product is bought from the supermarket, the contract is usually formed:

A) When the customer lifts the product off the shelf and puts the product into the basket.
B) When the customer holds onto the product for more than twenty minutes preventing other customers from buying that product.
C) When the customer takes the product to the cashier and offers payment.
D) When the cashier accepts payment for the product.