Question

One must do his duty. Correct the error

Answer 1

“One should Do Their Duty” is the right answer.

Because using the word must makes the sentence sound like an order rather than suggestions and using the word “him” personalizes the sentence to only male gender.

Every human being should do their own duty irrespective of your gender.

Answer 2

'One should do his duty'

is the correct sentence .

Because Must is used in command or in affirmative action.....using the word 'must' makes the sentence sound like an order rather than suggestion and so, we use 'should' but not 'must' .