[填空题]Alcoholism and{{U}} (1) {{/U}}addiction has already spread at alarming rate in the 21st Century. One of the biggest{{U}} (2) {{/U}}about it is that only{{U}} (3) {{/U}}people and ethnic minorities are more likely to get addicted. But the truth is that addiction is{{U}} (4) {{/U}}to{{U}} (5) {{/U}}, color and socio-economic background. People take drugs and alcohol because of the{{U}} (6) {{/U}}or relaxing effects they have on the body. But as the person develops a habit, the{{U}} (7) {{/U}}of the brain starts to change and adapt, {{U}} (8) {{/U}}more and more of the drug as it resists the discomfort of{{U}} (9) {{/U}}. The brain controls behavior by{{U}} (10) {{/U}}actions that will ensure survival of the species. But the problem lies in the fact that some chemicals, like caffeine, alcohol and{{U}} (11) {{/U}}can{{U}} (12) {{/U}}brain reward systems directly, {{U}} (13) {{/U}}the sensory receptors mediating natural rewards. But other more{{U}} (14) {{/