Final answer:
In the Cornell video about cancer, 'lack of exercise' was not described as an environmental risk factor that can affect our pets' development of cancer. The video mentioned factors including sunlight exposure, secondhand smoke, and air pollution.
Step-by-step explanation:
The Cornell video about cancer highlights various environmental risk factors that can affect our pets' development of cancer. The environmental risk factors described include exposure to sunlight, secondhand smoke, and air pollution. However, lack of exercise was not mentioned as an environmental risk factor in the video related to the development of cancer in pets. Regular exercise is indeed important for overall health, but it was not described as a direct environmental risk factor for cancer in this context.