Appearance of antibiotic-resistant bacteria is an example of

Options

A. adaptive radiation
B. transduction
C. pre-existing variation in the population
D. divergent evolution.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks us to identify what the appearance of antibiotic-resistant bacteria exemplifies among the given options: adaptive radiation, transduction, pre-existing variation in population, or divergent evolution.

2. **Defining Antibiotic Resistance**: Antibiotic-resistant bacteria are those that have developed the ability to survive exposure to antibiotics that would normally kill them or inhibit their growth.

3. **Analyzing the Population**: In a bacterial population, when exposed to antibiotics, some bacteria may have mutations that confer resistance. These resistant bacteria survive while the sensitive ones die off.

4. **Role of Mutations**: The resistant bacteria, having pre-existing variations (mutations), begin to multiply and dominate the population. This indicates that the resistance was not newly created but rather a result of variations that existed before the antibiotic exposure.

5. **Identifying the Correct Option**: Given that the appearance of antibiotic-resistant bacteria stems from these pre-existing variations in the population, we conclude that the correct answer is **C. Pre-existing variation in population**.

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