**Core Concept:** Cox are bacterial organisms, also known as bacteriophages, that infect and replicate within the host bacterial cells. The question is asking about the conditions under which cox cannot grow.

**Why the Correct Answer is Right:** Cox grow specifically within bacterial cells and cannot survive or multiply in other cell types such as egg or animal cells. These cells lack the necessary components required for cox to replicate, which are specific to bacterial cells.

**Why Each Wrong Option is Incorrect:**

A. Cox can grow in egg cells, but the question specifically mentions that they won't grow in egg cells, making this option incorrect.
B. Cox grow in animal cells, not in egg cells, making this option incorrect as well.
C. Cox grow in bacterial cells, not in egg cells, making this option incorrect.
D. Cox grow in egg cells, not in animal cells, making this option incorrect.

**Clinical Pearl / High-Yield Fact:** Cox are crucial in studying bacterial infections and can be used as a tool to control bacterial populations in various fields, such as agriculture (e.g., controlling bacterial diseases in crops) and medicine (e.g., treating bacterial infections in humans and animals).

**Correct Answer:** Cox won't grow in egg cells (Option C). The reason is that they require specific components found in bacterial cells for replication, which are not present in egg or animal cells, making them unable to grow in these environments.