**Core Concept**
Serum sickness is an immune-mediated disorder that occurs due to the formation of antibodies against foreign proteins in the serum, leading to an allergic reaction. This reaction is often seen after the administration of certain medications, such as antivenom or immunoglobulin preparations.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of serum sickness, which involves the formation of antibodies against foreign proteins. When foreign serum is injected, the body recognizes the proteins as non-self and mounts an immune response against them. This response leads to the activation of complement, release of histamine, and an influx of inflammatory cells, resulting in symptoms such as fever, rash, and joint pain. The reaction is a type of hypersensitivity reaction, specifically a Type III hypersensitivity reaction, which involves the formation of immune complexes.

**Why Each Wrong Option is Incorrect**
**Option B:** Injection with own serum is not associated with serum sickness, as the body recognizes its own proteins as self and does not mount an immune response against them.
**Option C:** Injection with normal saline is not associated with serum sickness, as normal saline does not contain foreign proteins that can trigger an immune response.
**Option D:** All of the above is incorrect, as serum sickness is specifically related to the injection of foreign serum, not own serum or normal saline.

**Clinical Pearl / High-Yield Fact**
It's essential to note that serum sickness can be prevented by gradually introducing foreign proteins into the body to minimize the risk of an immune response. This is why antivenom preparations are often administered slowly and under close observation.

**✓ Correct Answer: A. Injection with foreign serum**