Concept:The ozone hole refers to a thinning or depletion of the ozone layer in the stratosphere, not a complete absence.Explanation:The ozone layer is found in the lower stratosphere, about 10 to 30 km above Earth. It absorbs most of the Sun's harmful ultraviolet radiation. An ozone hole means the concentration of ozone in that region has decreased significantly, making the layer thinner. This depletion is mainly caused by chlorofluorocarbon (CFC) gases released from human activities. The term "hole" does not mean a complete opening, but a severe reduction in ozone thickness. Option C correctly describes this as a decrease in the thickness of the ozone layer in the stratosphere. Options A and D describe increases, which are incorrect. Option B is not correct because option C is accurate.Answer:C. decrease in thickness of ozone layer in stratosphere.