the rule for controls is that
a. controls are only necessary if you're not doing an experiment
b. everything should remain the same between experimental groups
c. there should be only one independent variable and one dependent variable
d. the only change we make between experimental groups is to the independent variable

sup bro, im dumb, but this is what i found xd

"the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface"