Answer: d. 70% to 90%
Step-by-step explanation:
Gamblers Anonymous was founded in 1957 to help people with a compulsive gambling problem get better. Sadly it has not been very effective with one of their main criticisms being that 70 - 90% of participants drop out and most time go back to gambling.
There have been additional treatments suggested such as therapy but it would seem that gambling brings abut an addiction that is quite tough to let go of.