Ascientist is investigating the effects of salinity on fish development. he places fertilized fish eggs in an aquarium that contains low salinity and observes their development. what factor would improve experimental design the most?

Control experiment

Explanation:

This a treatment of no change in the experiment whereby all variables ( usually the effects of the independent variable on the dependent variable) are well known.  The control experiment is used to compare the outcomes with those of other treatments so as to verify and validate the experiment ad its results.

In this experimenter, placing another equal amount of fertilised fish eggs, from the same batch, in the water of salinity levels equal to that it would find in its normal environment, would be the control experiment.  

the answer would be d

not sure if this is what you'r looking for eubacteria and archaebacteria