Final answer:
Observing public behavior when participants are not identifiable does not constitute human subjects research under the Common Rule, unlike activities involving identifiable information such as surveys, interviews, or clinical trials.
Step-by-step explanation:
The activity that would not constitute human subjects research under the Common Rule is observing public behavior when the participants are not identifiable. This scenario does not involve data that can be linked to individual participants, thus it falls outside the scope of what is typically considered human subjects research which requires informed consent and oversight by an institutional review board (IRB). Activities such as conducting surveys and interviews, or engaging in clinical trials do involve identifiable information and therefore constitute human subjects research under the Common Rule, which means they need to follow ethical guidelines including informed consent and IRB review.