A Natural Science Research Team Presented Arguments Explaining Which Factors

A natural science research team presented arguments explaining which factors it regards as relevant and exactly why each of the factors is potentially relevant to the hypothesis being investigated. This explanation represents which step in the scientific investigation?

A) Design a procedure to ensure that the data gathered will reveal the full range of possible observations.
B) Conduct the study or the experiment and gather the data.
C) Critique the findings.
D) Identify all the factors related to the hypothesis and the phenomenon of interest that it will be important to measure, control, or monitor.