**Core Concept:**
The question is asking about the dimensions of a mosquito net, which is primarily used to protect against mosquito bites and prevent transmission of mosquito-borne diseases like malaria, dengue, and filariasis. Mosquito nets are designed to cover a person's body while they sleep and should be large enough to prevent the mosquitoes from entering the net's spaces.

**Why the Correct Answer is Right:**
The correct answer, **D** (60x80 cm), refers to the dimensions of a standard, non-treated bed net. This size ensures that the net covers the entire bed, providing sufficient protection against mosquitoes. The net's dimensions should be wide enough to cover the sides of the bed and long enough to cover the person sleeping under it, preventing mosquitoes from entering the spaces between the net and the bed or the person's body.

**Why Each Wrong Option is Incorrect:**

A. **60x70 cm:** This size is too narrow, not covering the entire bed or the person adequately, thus not providing sufficient protection against mosquitoes.

B. **90x120 cm:** Although larger than the correct answer, this size is still not ideal as it may not cover the person's feet, leaving them vulnerable to mosquito bites.

C. **100x150 cm:** This size is excessively large and may not be practical to store or transport, making it an unsuitable option for widespread use, especially in resource-limited settings.

**Clinical Pearl:**
A mosquito net should be large enough to cover the entire bed and person to ensure effective protection against mosquitoes. In reality, the ideal dimensions for a bed net depend on the bed's size, but for simplicity, the recommended dimensions are **60x80 cm** for a standard bed. This size ensures adequate coverage and reduces the risk of mosquitoes entering the spaces between the net and the person's body or the bed. The correct size is essential for preventing mosquito bites and reducing the risk of mosquito-borne diseases like malaria, dengue, and Zika virus.