Choose the answer that best matches the word enclosed. Use context clues to determine the meaning of the word, if necessary.

For many (millennia), people believed Earth was flat.

1. reasons
1. thousands of years
3. generations of people
4. beliefs or propositions

2. thousands of years

The best answer that matches the word enclosed, "millennia," is option 2: thousands of years.

To determine the meaning of the word "millennia" and choose the best answer that matches it, we can use context clues. In the sentence, it mentions that "people believed Earth was flat" for many (millennia). From this context, we can infer that "millennia" refers to a long period of time.

Now let's analyze the answer choices:
1. Reasons: This does not match the meaning of "millennia" as it refers to the factors or justifications behind something.
2. Thousands of years: This matches the meaning of "millennia" as it represents a long period of time.
3. Generations of people: Though "generations" can also imply a long period of time, it does not specifically fit the context of the sentence.
4. Beliefs or propositions: This does not match the meaning of "millennia"; it refers to ideas or statements.

Based on the above analysis, the best answer that matches the word "millennia" is option 2: thousands of years.