Why Do Scientists Use Comparative Studies

Why do scientists use comparative studies?

A) Most species are all the same,so a comparative study can be used instead of performing an experiment.
B) Similar phenomena in other species or regions can provide clues to events being investigated.
C) Comparative studies can replace an observational study,saving time and money.
D) Scientists use comparative studies to prove a hypothesis.
E) Scientists use comparative studies for research to publish peer-reviewed papers.