Please hurry up .......

I think the answer is D.

You probably are looking for which type of study was conducted by nico to collect the data: there are basic two types of studies to collect the data: a) observational studyb) experimentin experiment, some treatments are applied to a group and effects are noticed and recorded. in observational study, no treatments are applied and the subjects are observed to collect the data.    in this case, nico is just observing the students as he walked around the cafeteria, so the type of study involved to collect the data is observational study.