To identify the part with an error, let's analyze each option:
Option A) "It is our duty" - This option is correct. It is grammatically and structurally correct.
Option B) "to put off our shoes" - This option is incorrect. The correct phrase should be "to take off our shoes." The phrasal verb "take off" is used to indicate the action of removing something from one's body, such as shoes or clothes.
Option C) "before entering the sanctum sanctorum of any temple or mosque" - This option is correct. It provides additional information about the action of taking off shoes before entering a temple or mosque.
Option D) "no error" - This option is incorrect. There is an error in option B, as mentioned above.
Based on the analysis, the correct answer should be Option B, as it contains the error.