Washington MAST (Mandatory Alcohol Server Training) Practice Exam

Driving under the influence (DUI) refers to operating a motor vehicle while under the influence of substances that can impair one's ability to safely operate a vehicle. While option A correctly includes all of the mentioned substances (intoxicating liquor, marijuana, and any drug) and acknowledges that they can have a combined influence, the other options are incorrect. Option B is too narrow as it only mentions intoxicating liquor and does not consider other substances that can impair driving ability. Option C is also too narrow as it only mentions marijuana, neglecting other potentially impairing substances. Option D is also incorrect because it only mentions prescription drugs and ignores the fact that intoxicating liquor and marijuana can also impair one's ability to drive safely. Therefore, option A is the most correct and comprehensive answer.