Pollution
Pollution wether it’s chemical or from trash can lead to many defects in the body. Pollution can cause harm to the lungs specifically by getting air trapped in the alveoli
If John stretched while his muscles were cold, the negative effect that could occur is that C. he could injure or pull a muscle.
It is always important that your muscles are "heated" before you start exercising so as to avoid hurting yourself.
There is no information to solve the question