**Core Concept**
Alzheimer's disease is a complex neurodegenerative disorder influenced by a combination of genetic, environmental, and lifestyle factors. These factors can increase an individual's susceptibility to developing the disease or accelerate its progression.

**Why the Correct Answer is Right**
Smoking is not a known predisposing factor for Alzheimer's disease. In fact, some studies suggest that smoking may have a protective effect against Alzheimer's disease, although this relationship is still being researched. The other options are recognized risk factors for Alzheimer's disease. Individuals with Down syndrome are at a higher risk due to the presence of an extra copy of chromosome 21, which carries the gene for amyloid precursor protein (APP). Low education level has been linked to an increased risk of developing Alzheimer's disease, possibly due to reduced cognitive reserve. Female sex is also a recognized risk factor, with women being more likely to develop Alzheimer's disease than men.

**Why Each Wrong Option is Incorrect**
**Option A:** Down syndrome is a known risk factor for Alzheimer's disease due to the genetic predisposition associated with the extra copy of chromosome 21.
**Option B:** Low education level is a recognized risk factor for Alzheimer's disease, possibly due to reduced cognitive reserve.
**Option D:** Female sex is also a recognized risk factor, with women being more likely to develop Alzheimer's disease than men.

**Clinical Pearl / High-Yield Fact**
Individuals with Down syndrome are at a higher risk of developing Alzheimer's disease due to the presence of an extra copy of chromosome 21, which carries the gene for amyloid precursor protein (APP).

**✓ Correct Answer: C. Smoking**