D. when designing an experiment to test a hypothesis
Explanation:
A. before forming a hypothesis: A background research of the previous research studies as well as the literature review is to be done before constructing a hypothesis.
C. after generating an idea from an observation: After generating an idea from the observation other methodology should be implemented so as to rectified the fact that the observation is correct.
D. when designing an experiment to test a hypothesis: While implementing a suitable scientific methodology a research is required to be done so as test the hypothesis by an accurate and valid procedure.
