What Is the Purpose of a Market-Tracking Study

What is the purpose of a market-tracking study?

A) to determine if consumers switched brands from one time period to the next
B) to measure some variable of interest,such as market share or unit sales over time
C) to determine the relationship among several variables
D) to search for and interpret existing information relevant to the research problem
E) to keep up with changes competitors are making in their marketing mixes