**Core Concept**

A defective virus is a type of virus that is unable to replicate on its own due to a lack of essential genes. This is often due to a genetic mutation or deletion that renders the virus unable to produce essential proteins or enzymes necessary for its replication. Defective viruses rely on a helper virus to provide the necessary genetic material and proteins for replication.

**Why the Correct Answer is Right**

The correct answer is a defective virus because it lacks the necessary genes to produce viral enzymes, such as reverse transcriptase, or other essential proteins required for its replication. This results in the virus being unable to replicate independently and relies on a helper virus to provide the necessary genetic material and proteins for replication. The helper virus can provide the necessary genetic material and proteins for the defective virus to replicate, making it a dependent virus.

**Why Each Wrong Option is Incorrect**

**Option A:** This option is incorrect because it does not provide any information about the virus being defective. A defective virus is specifically characterized by its inability to replicate on its own due to a lack of essential genes.

**Option B:** This option is incorrect because it describes a virus that is capable of replication on its own, making it a non-defective virus.

**Option C:** This option is incorrect because it describes a virus that is capable of replication on its own, making it a non-defective virus.

**Clinical Pearl / High-Yield Fact**

A key characteristic of defective viruses is their inability to replicate on their own, making them dependent on a helper virus for replication. This can result in a complex interplay between the defective and helper viruses, leading to unique replication and transmission patterns.

**Correct Answer:** C.