To effectively support the text regarding the impact of aggressive logging practices in South America's rain forests on global air quality, particularly through the trees' role in photosynthesis, option A. A diagram that explains the process of photosynthesis would be the best choice.
This graphic would directly illustrate how trees convert carbon dioxide into oxygen, which is central to the scientist's argument about the negative effects of logging on air quality. While the other options provide relevant information, they do not directly articulate the biological process necessary to understand the connection between logging and its impact on air quality.