Caterpillar needed to know what truck fleets should test their two new engines; how they could get a marketing strategy that could be measured; and how to adjust for the coming downturn in sales. To answer these questions, they gave their salesforce laptops and paid them to enter customer information related to each sale they made. Caterpillar analyzed the newly acquired customer data and developed strategies to address their marketing questions. Caterpillar utilized ________.

a. secondary marketing
b. external marketing
c. database marketing
d. internal marketing