Which of the Following Is the Best Definition of Research

Which of the following is the best definition of research?

A) Research is critically thinking about problems that occur in health care to determine possible solutions.
B) Research is information that is based on personal experience or tradition.
C) Research is planned and systematic activity that leads to new knowledge and/or the discovery of solutions to problems or questions.
D) Research is trying a variety of approaches to a clinical problem and settling on the approach that is effective most of the time.