**Core Concept**
Civil negligence is a type of tort law where a person is held liable for causing harm or injury to another due to a failure to meet the standard of care. In this context, the onus of proof refers to the burden of providing evidence to support a claim.

**Why the Correct Answer is Right**
The onus of proof in civil negligence lies with the plaintiff (the person making the claim), who must demonstrate that the defendant (the person being sued) was negligent and responsible for the harm or injury. This requires the plaintiff to provide sufficient evidence to prove that the defendant failed to meet the standard of care and that this failure caused the harm or injury. The plaintiff must establish a clear link between the defendant's actions (or lack thereof) and the resulting harm or injury.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the onus of proof in civil negligence does not lie with the defendant, who is typically required to defend themselves against the plaintiff's claims.
* **Option B:** This option is incorrect because the onus of proof in criminal law, not civil negligence, typically lies with the prosecution (the state or government).
* **Option C:** This option is incorrect because the onus of proof in administrative law, not civil negligence, may lie with the administrative body or agency being challenged.

**Clinical Pearl / High-Yield Fact**
In tort law, the onus of proof is a critical concept that can have significant implications for patients, healthcare providers, and the justice system as a whole. Understanding the onus of proof can help healthcare providers navigate complex legal situations and avoid potential liability.

**Correct Answer: A. The plaintiff.**