Final answer:
Marketing professionals can obtain secondary data for free from commercial research firms, which is nonreactive or unobtrusive, meaning it does not involve direct contact with subjects and does not influence their behavior. None of the options are the right answer.
Step-by-step explanation:
Marketers can purchase secondary data, which is secondary data available for free from commercial research firms. Secondary data is data that has been collected for some other purpose but can be used for the current research as well. This type of data is nonreactive or unobtrusive research, meaning it does not involve direct contact with subjects, and therefore, does not alter or influence people's behaviors. This is the advantage of secondary data over primary data, which requires direct contact and can be more costly and time-consuming to collect.
Using secondary data is considered an unobtrusive or nonreactive form of research. An example of this is the data from old movies or World Health Organization (WHO) statistics, which can be used without the need to enter a population or the investment and risks inherent in primary research processes.