Explanation:

- The sentence talks about how "they" acted in a past difficult situation. This means we need a past tense verb.

- Option 1: "behaves" is present tense. It doesn't fit because the situation mentioned is in the past.

- Option 2: "behaved" is past tense. It matches the need for past action in the sentence.

- Option 3: "behaving" is a continuous form and does not fit the sentence structure.

- Option 4: "belief" is a noun, not a verb, and doesn't make sense in this context.