Graphite is used in a nuclear reactor as

Options

A. a moderator
B. a fuel
C. an electrode
D. a lubricant

Explanation

**Step-by-Step Solution:**

1. **Understanding the Function of Graphite in Nuclear Reactors:**
- In a nuclear reactor, the primary goal is to sustain a controlled nuclear chain reaction. This involves the interaction of neutrons with nuclear fuel.

2. **Identifying the Role of Graphite:**
- Graphite is a form of carbon that has unique properties, particularly its ability to slow down fast-moving neutrons. This slowing down is crucial because it increases the likelihood of neutrons being captured by the nuclear fuel, which is typically uranium or plutonium.

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