**Core Concept**
The period of onset in tetanus refers to the time between the incubation period and the onset of symptoms. The incubation period is the time elapsed between the exposure to the tetanus spores and the appearance of the first symptoms. This concept is crucial in understanding the pathophysiology of tetanus and is essential for diagnosis and management.

**Why the Correct Answer is Right**
The correct answer is based on the clinical definition of the period of onset in tetanus. The incubation period is the time between exposure to the tetanus spores and the onset of symptoms, which can range from 3 to 21 days. The period of onset is a critical factor in diagnosing tetanus, as it helps clinicians to determine the severity of the disease and plan appropriate treatment. The period of onset is directly related to the time it takes for the tetanus spores to colonize the wound and produce the tetanospasmin toxin, which is responsible for the characteristic muscle spasms and rigidity of tetanus.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the period of onset in tetanus refers specifically to the time between the incubation period and the onset of symptoms, not the time between the exposure to the tetanus spores and the peak severity of symptoms.
* **Option B:** This option is incorrect because the period of onset in tetanus is a distinct concept that refers to the time between the incubation period and the onset of symptoms, not the time between the exposure to the tetanus spores and the resolution of symptoms.
* **Option C:** This option is incorrect because the period of onset in tetanus is a clinical concept that refers to the time between the incubation period and the onset of symptoms, not the time between the exposure to the tetanus spores and the development of complications.

**Clinical Pearl / High-Yield Fact**
The period of onset in tetanus is a critical factor in diagnosing and managing the disease, and clinicians should be aware of the typical range of incubation periods (3-21 days) to accurately diagnose and treat tetanus. A mnemonic to remember the typical range of incubation periods is: "3-21 days: Tetanus Always Takes Time".

**Correct Answer:**
Correct Answer: C.