Why are some barriers in avoiding alcohol, drugs and tobacco?

In which way does nicotine cause addiction? by stimulating the brain's pleasure center by increasing blood-sugar levels by decreasing dopamine levels by reducing depression and anxiety

Does indrect sunlight does not pose any danger to the skin

Viral infections in plants ) can be controlled with antibioticsb) can spread within a plant via plasmodesmata c) have little effect on plant growthd) are not spread by animals