Answer:
The answer is: A) raises GDP.
Explanation:
If a gambler is a professional gambler (pays income tax on his gambling earnings) then when he moves from a state that prohibits gambling to a state that allows gambling, his earnings will increase the GDP.
The GDP only considers legal income, so illegal activities such as prostitution, drug trafficking, or illegal gambling are not included in the GDP. But if they become legal (e.g. some states legalized marijuana) then they should be included in the GDP.