The correct option is the last one: "The organism (zebrafish shares its physiology with humans..." This is importante, since several drugs or experimental treatments, whose consequences are unpredictable, are able to be tested without harming people. Assessing risk-effectiveness of new treatments is critical for the final decision upon they will be massively used or not. Besides, zebrafish is a low cost organism that could be maintained with few cares and it can produce a lot of individuals, which is desirable in scientific experimental design.