How do genetics (genetic predisposition) and the environment work together to cause substance abuse in individuals? What is the likely role of epigenetics in this process?

I could be wrong but id say

Genetics is the study of genes. Genes are functional units of DNA that make up the human genome. They provide the information that directs a body's basic cellular activities. Research on the human genome has shown that, on average, the DNA sequences of any two people are 99.9 percent the same. However, that 0.1 percent variation is profoundly important. t accounts for three million differences in the nearly three billion base pairs of DNA sequence. These differences contribute to visible variations, like height and hair color, and invisible traits, such as increased risk for or protection from certain diseases such as heart attack, stroke, diabetes, and addiction. Genetics and lifestyle factors—such as diet, physical activity, and stress—affect high blood pressure risk. NIDA research has led to discoveries about how a person's surroundings affect drug use in particular. For example, a community that provides healthy after-school activities has been shown to reduce vulnerability to drug addiction, and data show that access to exercise can discourage drug-seeking behavior, an effect that is more pronounced in males than in females.

b. as prices rise, quantity demanded goes down.