The answer is C, since antibiotics will not effect viruses, only bacterial infections.
Radon and Thoron are the most significant sources of radiation exposure to people living in the United States accounting for 37% of total radiation exposure.
These are nuclides that are produced from the radioactive decay of materials especially in consumer products and through natural processes such as the decay of radium.
The independent variable is the variable that is being changed in an experiment. It is also called the manipulated variable. In this case, it would be the amount of sunlight. The dependent variable would be the variable that is being studied. In this case it would be the length of sleep of the mice. The constants would be the variable that are supposed to have an effect on the dependent variable however it is held constant so as to clearly see the effect of the independent variable.