According to the federal regulations, which of the following studies meets the definition of research with human subjects?

A. A researcher conducts a comparison of the comments made in a publicly available blog and the blogger's comments on a similar topic in a weekly magazine.
B. A researcher sets up a meeting with the superintendent of a large and diverse public school system to get data about the ethnic composition of the school system and the number of students receiving free lunches.
C. A cognitive psychologist enrolls undergraduate students for a computer-based study about the effect of mood on problem solving behaviors.
D. Undergraduate students in a field methods class are assigned a research question and asked to interview another classmate, to be followed by a class discussion on interview techniques.