Marketing studies refer to the analysis of the relationships and variables involved in the markets, for which different statistical tools are used, marketing studies have several purposes, according to the approach sought by the study you can investigate whether a certain product of the market is known, if it is considered expensive or economical, if the population would be willing to buy a new product or because it would stop buying an existing one, if the advertising used for current sales has good results, among other multiple investigations that can be make.
In this case, as the product already existed in the market and had a sales trend, the first thing the manager should do when noticing the change in sales is to try to identify the reasons for the problem, before trying to experience a solution that does not come of data.
Answer
C. The manager should first do marketing research to identify what needs were not being satisfied.