Select the most appropriate synonym of the underlined word.
The hypothesis that the police believed in led to a lot of chaos.

The correct answer is speculation.

Step-by-step Explanation:

1. Understand the underlined word:
The word hypothesis refers to a proposed explanation, theory, or assumption made on the basis of limited evidence as a starting point for further investigation. In the context of the sentence, it refers to a theory or guess that the police believed without concrete proof, which ultimately led to chaos.

2. Analyze the options:

• speculation: The forming of a theory or conjecture without firm evidence. This is highly synonymous with "hypothesis" as both involve unproven assumptions or guesses.
• breakthrough: An important discovery or development that helps to solve a problem. This is not synonymous with hypothesis.
• trepidation: A feeling of fear, alarm, or agitation about something that may happen. This has no relation to hypothesis.
• encounter: An unexpected or casual meeting with someone or something. This is unrelated to hypothesis.

3. Conclusion:
Since "speculation" directly matches the meaning of an unproven theory or assumption, it is the most appropriate synonym for "hypothesis" in this context.