I think it is all of the above but you might want a second opinion.
The changing quantities in an experiment are called variables. A variable refers to any trait, factor, or a condition, which can prevail in distinct amounts or kinds. An experiment generally exhibits three kinds of variables: independent, dependent, and controlled.
The independent variable refers to the one, which is modified. On the other hand, the dependent variable is implied to observe that how it reacts with the change made to the independent variable. The controlled variables refer to the quantities, which one wants to remain constant.
In the given case, that is, heating a cup of water to witness that whether the sugar will get more easily dissolve. In this, the independent variable refers to the temperature of the water determined in degrees Centigrade. The dependent variable refers to the amount of sugar, which dissolves completely measured in grams.
In this, the controlled variables are stirring and type of sugar. As more stirring might elevate the amount of sugar that dissolves, and different kind of sugars might dissolve in distinct concentrations. So, in order to make sure a fair test, there is a need to keep these variables similar for each cup of water.
Answer: Plants
Explanation: Less solar radiation would mean less sunlight for photosynthesis which means that they won't get enough energy for survival and might die out.
Melanin provides pigmentation to the skin and it also provides UV ray protection (which is its role in the epidermis).
I think the answer here is neurons, the nerve cells
