Identify the part of the sentence that needs to be corrected.
Before they/ were caught / they were used to live / in the jungle

Key Points:
The incorrect phrase in the sentence is "they were used to live".
The correct form should be "they used to live".
Correction:
Before they were caught, they used to live in the jungle.

"Used to + verb" is the correct structure to indicate a past habit.
"Be used to" means being accustomed to something, which does not fit in this context.
Why is Option C incorrect?
Incorrect: "they were used to live"
Correct: "they used to live"
Explanation:

"Used to + base verb" is used to talk about past habits or states.
Example: "He used to play football."
"Be used to + noun/gerund" is used to indicate familiarity with something.
Example: "He is used to waking up early."
Since the sentence describes a past habit, "used to live" is correct.