Sleep is prevented by:

Options

A. Valium
B. barbiturates
C. amphetamines
D. benzodiazephines

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about substances that prevent sleep.

2. **Identifying the Substance**: According to the video transcript, one of the primary substances mentioned that prevents sleep is **Amphetamine**.

3. **Mechanism of Action**: Amphetamines work by stimulating the central nervous system. They send signals that counteract feelings of sleepiness, effectively keeping a person awake.

4. **Other Substances**: The transcript also mentions **barbiturates** and **benzodiazepines**. However, these are typically used to induce sleep or sedation rather than prevent it.

5. **Conclusion**: The main substance identified that prevents sleep is **Amphetamine**.

### Final Answer:
Sleep is prevented by **Amphetamine**.

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