In One-To-One Marketing,what Is the Next Step After a Marketer

In one-to-one marketing,what is the next step after a marketer has identified customers and knows them in as much detail as possible?

A) interact with the customers and find ways to improve cost efficiency
B) make efficiency of interactions with customers the priority
C) differentiate among these customers in terms of both their needs and their value to the company
D) customize some aspects of the products or services offered to each customer
E) implement a mass customization program