Answer: C. The temperature of the water.
Step-by-step explanation:
In an experimental setup, an independent variable is the one which can be manipulated so as to know it's impact over the dependent variable. The dependent variable is the outcome of the experiment.
In the given example, the temperature of the water is the independent variable which can be changed or manipulated in the experiment manually so as to know it's impact over the dissolution of sugars in water.