Which is not a sign of nicotine addiction

How do the uv rays cause damage?   what exactly causes the skin to burn;   can you be more specific about this mechanism?   3. how do photosensitive medications increase a person's sensitivity to sunlight and therefore increase their risk of getting burned?     what kind of medications can increase photo-sensitivity, can you think of some examples?

Which of these is a controllable risk fator for disease

Who is considered the father of modern behavioralism? a fred b jung simmer pavlov