Answer: Option D
Step-by-step explanation: In simple words, those research whose subject are not humans are called not human subject researches. Although humans could be used as a source of information for conducting research and gathering information,but the research revolves around some other object or phenomenon.
In the given case, candidate is planning to research on the junk food availability in the market and is collecting information from local stores owned by humans.
Hence from the above we can conclude that the correct option is D.