Answer:
c. comparability of data
Explanation:
One of the problems that Harry is likely to face in this situation would be related to the comparability of data. In this example, Harry will use the information that has been gathered by several different independent market research agencies. It is likely that all of these agencies employ slightly different methods to gather data and even focus on different research questions. Therefore, it might prove difficult for Harry to design a way in which all this very different information can be compared and analyzed.