Which of the following can be researched using a quantitative approach?

Non-participant observation of performance of a group of students in a laboratory

Studying a phenomenon in depth as it occurs in nature

Starting the exploration of a problem with a broad idea and continuously modifying the design as the researcher proceeds with data collection

Generating new questions from every member of the sample and presenting the findings in informal language

Conducting and recording long and in-depth interviews and transcribing the verbatim to identify themes for reporting as the findings of the research