**Core Concept**
The Aedes aegypti index, also known as the Aedes aegypti infestation index or the Breteau index, is a measure of the prevalence of Aedes aegypti mosquitoes in a given area. This index is used to assess the risk of yellow fever transmission in a region.

**Why the Correct Answer is Right**
The Aedes aegypti index is calculated by dividing the number of positive breeding sites by the total number of houses in a given area, multiplied by 100. A higher index value indicates a greater prevalence of Aedes aegypti mosquitoes, which are the primary vectors of yellow fever. The correct index value is 3, indicating a moderate risk of yellow fever transmission.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide a valid index value. The Aedes aegypti index is a measure of the prevalence of Aedes aegypti mosquitoes, and a value of 0 would indicate no mosquitoes present, which is not a feasible scenario.

**Option B:** This option is incorrect because it does not provide a valid index value. The Aedes aegypti index is a measure of the prevalence of Aedes aegypti mosquitoes, and a value of 10 would indicate a very high risk of yellow fever transmission, which is not the correct answer.

**Option C:** This option is incorrect because it does not provide a valid index value. The Aedes aegypti index is a measure of the prevalence of Aedes aegypti mosquitoes, and a value of 5 would indicate a moderate to high risk of yellow fever transmission, but it is not the correct answer.

**Clinical Pearl / High-Yield Fact**
The Aedes aegypti index is a crucial tool for public health officials to assess the risk of yellow fever transmission in a region. It is essential to monitor this index regularly to implement control measures and prevent outbreaks.

**Correct Answer: D. 1**