Explanation : In experimental research, the essential processes are:
✅ Observation — to note effects of the experiment
✅ Manipulation and replication — manipulating variables and repeating to check reliability
✅ Controlling — controlling extraneous variables to ensure internal validity
However, reference collection (i.e., gathering reference materials or literature) is not an actual process step of conducting an experiment itself, though it can support the background.
So the correct answer is: D. Reference collection
usha on (2025-06-26 21:36:22) Comments : the answer does not suit well because manipulation is criteria or characteristic of experimental research
reference collection or observation would be a better answer