The correct answer is C. Trial and error.
Research is a systematic process of gathering and analyzing information to answer a question or solve a problem. It is an objective process that is based on evidence and reasoning. Trial and error is not a systematic process, as it is based on trial and error rather than evidence and reasoning.
A. Systematic activity: Research is a systematic process that involves a series of steps, such as identifying the problem, gathering information, analyzing the information, and drawing conclusions.
B. Objective observation: Research is an objective process that is based on evidence and reasoning. Researchers must avoid bias and personal opinions in their research.
D. Problem solving: Research is a problem-solving process that involves identifying a problem, gathering information about the problem, analyzing the information, and developing solutions to the problem.
In conclusion, the correct answer is C. Trial and error.