Explanation:

- Option 1: threaten - This means to express an intention to inflict harm or damage. It doesn't fit the context as it's unlikely the sentence is about intimidating the people.

- Option 2: bluster - This means to talk in a loud, aggressive, or indignant way with little effect. This might not fit well unless the context is about someone speaking with bluster to the people.

- Option 3: blow - This means to move creating an air current or sound. In terms of people and context, it doesn't seem relevant here.

- Option 4: sustain - This means to strengthen or support physically or mentally. It's an appropriate word if the context is about helping or supporting the people.

Considering the likely context of the sentence, if it is about support or helping, then:

- Correct Answer: sustain