Which of the Following Methodological Approaches to a Research Project

Which of the following methodological approaches to a research project on same-sex parent families would be an experiment?

A) A researcher conducts a series of interviews with same-sex and heterosexual families to understand choices surrounding insemination,surrogates,and adoption.
B) A researcher distributes paper questionnaires to same-sex families asking them about their household and children.
C) A researcher examines the differences in same-sex couples' adoption practices in the United States vs.Europe.
D) A researcher sends two sets of parents out to interact with others in a coffee shop and find out how people respond to one of two conditions: a gay couple with a crying male baby,and a heterosexual couple with a crying male baby.