**Core Concept**
Primary prevention aims to prevent the occurrence of a disease or injury before it happens, often through measures such as vaccination, lifestyle modifications, or environmental interventions. This approach focuses on removing the root cause of the disease to prevent its onset.

**Why the Correct Answer is Right**
The use of mosquito nets is a prime example of primary prevention. By using a mosquito net, an individual can prevent themselves from being bitten by mosquitoes that transmit diseases like malaria. This intervention occurs before the onset of the disease, thereby preventing its occurrence. The use of mosquito nets is a simple, effective, and evidence-based measure that reduces the risk of malaria transmission.

**Why Each Wrong Option is Incorrect**
**Option A:** Screening tests, on the other hand, are a form of secondary prevention. They aim to detect diseases in their early stages, often through diagnostic tests or examinations, to prevent further complications. Screening tests do not prevent the disease from occurring in the first place.

**Option B:** Early diagnosis is also a form of secondary prevention. While early diagnosis allows for timely treatment and intervention, it does not prevent the disease from occurring in the first place. Early diagnosis is a reactive approach that responds to the disease after it has already begun to manifest.

**Option D:** Restoration of lost function is a form of tertiary prevention. Tertiary prevention focuses on reducing the impact of an ongoing illness that has lasting effects, often through rehabilitation or maintenance therapy. This approach does not prevent the disease from occurring in the first place but rather aims to mitigate its effects after it has already begun.

**Clinical Pearl / High-Yield Fact**
Remember the ABCD framework for prevention: A (primary prevention) aims to prevent disease occurrence, B (secondary prevention) aims to detect disease early, C (tertiary prevention) aims to reduce disease impact after it has occurred.

**✓ Correct Answer: C. Use of mosquito net**