Explanation

• The whole nation was behind the president. پوری قوم صدر کے پیچھے کھڑی تھی۔
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• behind preposition (BACK)
• at or to the back of someone or something:
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• "The whole nation "at the back of the president. 
• so the "behind" is the best option to keep the meaning of original sentence

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  ND16-12-2022