Dichotomous keys consist of a series of statements with two choices in each step that will lead users to the correct identification. So I believe your answer would be A.
The correct answer is C. The water is the solvent because the green pellets dissolved in it.
Explanation:
In solutions, the are two substances involved, the solvent and the solute. The solvent is usually a liquid substance; additionally, the solvent dissolves another substance, which is known as the solute. For example, if you dissolve a spoon of salt in a glass of water, the solute is the salt which is the substance dissolved and the solvent is the water because the solute is dissolved in it. According to this, in the case presented the water is the solvent because the green pellets which are the solute dissolve in it.
