Which of the Following Is True About Missionary Salespeople

Which of the following is true about missionary salespeople?

A)  They are used in certain industries to focus exclusively on promotion of existing products and introduction of new products.
B)  They are used when the product is extremely high priced and is being sold to the whole organization.
C)  They provide training to the front-line staff of the buying organization.
D)  They are especially useful when the product is to be used to solve certain technical problems of the buyer.