Explanation:

- Option 1: Although

- This option is used to introduce a contrast between two statements. Even though the boys were scared, they chose to remain in the jungle. It fits the context well.

- Option 2: Because

- This option is used to provide a reason for something. If used here, it would imply the boys stayed because they were afraid, which does not make logical sense.

- Option 3: In case

- This is used to indicate a precaution against something. It doesn’t fit the sentence structure or meaning.

- Option 4: So that

- This is used to convey purpose. It would suggest the boys were afraid for the purpose of staying, which doesn’t logically connect.