The correct answer is letter A. The disk soaked in distilled water is the controlled variable because it is the only differential factor from all of the other variables which are all disinfectants. Controlled variables are elements that are not changed throughout the experiment. When something is unchanged it is better for scientists to analyze the relationships of other variables better.
Lava rock contain a fossil
A nucleophilic addition-elimination reaction between the carboxylic group and the amino group bonds the amino acids together.
They can be observed in a microscope because both of them are very small to see. Mostly, they contain genetic material. Viruses need a host to keep it spreading or etc.
Longitudinal studies make comparisons over time, whereas cross-sectional studies make comparisons at a single point in time. hope that helps some
