**Core Concept**
Diabetes mellitus is a metabolic disorder characterized by hyperglycemia, resulting from either insulin deficiency or insulin resistance. The symptoms of diabetes are primarily due to the effects of high glucose levels on various bodily functions.

**Why the Correct Answer is Right**
The symptoms of diabetes mellitus are a result of the body's inability to utilize glucose properly. High glucose levels lead to increased glucose excretion in the urine (glycosuria), causing osmotic diuresis and subsequent dehydration. This dehydration can cause symptoms such as thirst (polydipsia), dry mouth, and increased urination (polyuria). Additionally, the high glucose levels can damage blood vessels and nerves, leading to symptoms such as blurred vision, fatigue, and numbness or tingling in the hands and feet.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because while it is true that diabetes is a risk factor for certain infections, it is not a direct symptom of the disease.

**Option B:**
This option is incorrect because while weight loss is a common symptom of type 1 diabetes, it is not a universal symptom of diabetes mellitus, and may not be present in all cases of type 2 diabetes.

**Option C:**
This option is incorrect because while hypertension is a common comorbidity in patients with diabetes, it is not a direct symptom of the disease.

**Clinical Pearl / High-Yield Fact**
A classic presentation of diabetes mellitus is the "3 Ps": polyuria, polydipsia, and polyphagia (increased hunger).

**Correct Answer: A. This option is incorrect because while diabetes is a risk factor for certain infections, it is not a direct symptom of the disease.**