Answer: Option a
Explanation: In simple words, it refers to the traditional method of selling under which the organisation hires sum people to directly interact with the customers and persuade them to buy the product. These sales personnel uses their specialized knowledge, appearance and attitude to manipulate customers.
In such a method, the individual is the only entity from which the potential customer interacts and are responsible for the services that are needed to be performed after the order is made.
Hence the correct option is A.