**Core Concept**
The Centers for Disease Control and Prevention (CDC) defines a past smoker as an individual who has smoked at least 100 cigarettes in their lifetime but has not smoked in the past 12 months. This definition is crucial for epidemiological studies and public health surveillance.

**Why the Correct Answer is Right**
The CDC's definition of a past smoker is based on the number of cigarettes smoked and the duration of smoking cessation. The 100-cigarette threshold is arbitrary but helps distinguish between current and former smokers. The 12-month period of abstinence is used to ensure that individuals have made a significant effort to quit smoking.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because it does not specify the number of cigarettes smoked or the duration of smoking cessation.
**Option B:** This is incorrect because it does not accurately reflect the CDC's definition of a past smoker.
**Option C:** This is incorrect because it implies that the individual has never smoked, which is not the case for a past smoker.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the CDC's definition of a past smoker is used for surveillance and research purposes, and it may not be applicable in all clinical settings. When assessing a patient's smoking history, it's crucial to consider their individual circumstances and medical history.

**Correct Answer:** Not provided