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Help im confused

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?

Measuring your progress by weight (only)? a: the fit of your clothes b: bathroom scale c: body fat scale d: body fat caliper

What is the function of the retina?