Carl Is a Junior in College

Carl is a junior in college. Over the last 12 months, he has spent his weekends drinking alcohol and playing poker. He does not drink on weekdays but occasionally uses amphetamines to stay awake during the all-night poker games. He then takes Valium so that he can sleep during the day and be rested for the next night's game. Carl's friends are worried that Carl is hooked on drugs and that he can't stop, but Carl claims he has no problem with his drug use. Carl boasts that he can drink more beer now than he could when he first came to college without becoming as intoxicated or having a hangover the next day. He dismisses the risks associated with mixing alcohol with other drugs like Valium, stating that only people who don't know what they are doing have problems. Carl attends his classes, although he has been missing the early Monday class, and his overall grade-point average has dropped this semester.
-Carl's biggest health risk from his current pattern of drug use is

A) respiratory depression.
B) amphetamine-induced psychosis.
C) flashbacks.
D) alcoholism.