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.
scientific names known over all word or as internationaly
Yes a plant is taking a food from earth. Some plant like different food that has different PH level, than others therefore if you change the soil on the same plant it effects it's growth.
Answer:
Air is forced to rise over mountains, air cools and condensation occurs, rain falls over the mountains, dry air sinks down the other side of the mountain. Some deserts form in areas that lie at great distances from the sea. The air here is much drier than on the coast.
Explanation:
