The answer is: B. It ensures that the quality of scientific research is maintained.
Peer review is used to maintain quality standards, point to sources of error and improve performance.
Work on project is evaluated by people with similar competences (qualified members of a profession within the relevant field) as the scientist who are performing the work.
It is common in the field of health care.
Consensus is achieved through communication at conferences, the publication process, replication and peer review.