填空题

Alcoholism and 1 addiction has already spread at alarming rate in the 21st Century. One of the biggest 2 about it is that only 3 people and ethnic minorities are more likely to get addicted. But the truth is that addiction is 4 to 5 , color and socio-economic background.
People take drugs and alcohol because of the 6 or relaxing effects they have on the body. But as the person develops a habit, the 7 of the brain starts to change and adapt, 8 more and more of the drug as it resists the discomfort of 9 .
The brain controls behavior by 10 actions that will ensure survival of the species. But the problem lies in the fact that some chemicals, like caffeine, alcohol and 11 can 12 brain reward systems directly, 13 the sensory receptors mediating natural rewards. But other more 14 drugs, such as heroine and cocaine, can produce a far more 15 effect, so the addiction would be more 16 .
Addictions are lifelong 17 that are very hard to get rid of. Even some of the most skilled and 18 people might become addicts even though they are fully 19 of their harmful nature. The biggest killer is the person"s 20 of his or her condition of getting slowly addicted.