Explanation:

- Debilitate: This word means to make someone or something weak or feeble. It reflects a reduction in strength or energy.

- Option 1: Sustain - This means to support, maintain or keep something going. It has a positive connotation and implies strength, not weakness.

- Option 2: Weaken - This is a direct synonym to debilitate. It means to reduce strength, effectiveness, or energy.

- Option 3: Animate - This means to bring to life or to give spirit. It contrasts with debilitate as it suggests vitality.

- Option 4: Vitalise - Similar to animate, it means to give life or energy to something. It also has the opposite effect of debilitate.

- Correct Answer: Option 2: Weaken

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