Answer:
D. obtaining a commitment from the customer.
Explanation:
Closing a sale is the equivalent of making a sale.
To consider a sale done, you need to have a commitment from the customer to buy the product/service you're offering. That usually mean receiving money or at least firming a binding contract.
None of the other options is describing a complete sale. A and C are potential leads/sales... while B if of course the opposite of closing a sale.
