All residents in the community were advised that they \_\_\_\_ in order to prevent the contagion.

符合「advise that」後接假設語氣「(should) + 原形動詞」的規則，使用原形動詞「adhere」，並正確搭配介系詞「to」與名詞片語「social distancing」（社交距離措施）。