The independent variables, the ones that are intentionally manipulated are (A) temperature and surface area. The dependent variable, the one that you measure the response in, is (C) reaction time.
Explanation
If the variables of an experiment are temperature, surface area and reaction time or rate of reaction, then the independent variables will be temperature and surface area and dependent variable will be rate of reaction or reaction time.
This is because, reaction time also known as the rate of reaction is the time required to complete the whole chemical process, generally depends on factors like, temperature, phase, surface area, concentration of reactants etc.
So the dependent variable will be the one which is affected by other factors which will act as independent variables.
It is also known that the reaction time decreases as there is increase in temperature and surface area of the reactants.
So the experiment can be carried out using temperature and surface area as independent variables such that they can be intentionally manipulated and reaction time will be the dependent variable which will be varied or affected by the change in temperature and surface area.
