What is the strongest evidence that HCFCs are in the stratosphere? (A) A) Measurement of HCFCs in air samples from the stratosphere. (B) B) Satellite measurements of light passing through the atmosphere. (C) C) Measurement of chlorine in air samples from the lower atmosphere. (D) D) Chemical reactions predict there should be HCFCs in the upper atmosphere.

The strongest evidence that HCFCs are present in the stratosphere comes from **direct measurements** of these compounds in that specific atmospheric layer. **Option A: Measurement of HCFCs in air samples from the stratosphere** is the most direct and robust evidence. By collecting air samples from the stratosphere and analyzing them for HCFC concentrations, scientists can conclusively confirm the presence of these substances in that region of the atmosphere. **Other Options:** - **Option B:** While satellite measurements provide valuable data about atmospheric composition, they often rely on indirect methods such as spectroscopy, which may not be as precise as direct sampling. - **Option C:** Measuring chlorine in the lower atmosphere can indicate potential sources but doesn't directly confirm the presence of HCFCs in the stratosphere. - **Option D:** Chemical reactions predicting the presence of HCFCs offer theoretical support but do not provide concrete evidence. **Therefore, the best answer is:** **Answer:** (A) Measurement of HCFCs in air samples from the stratosphere.