If you feel it is the duty of others to refute the claim, and not of yourself to support it, then how about refuting the existence of invisible pink unicorns?
It is congress's duty to oversee the spending of federal funds.
An ambassador died in the line of duty when his car was ambushed.
Used in the Ending of Sentence
Cicero's writing treats mainly of old age and personal duty.
The young Marine was spoiling for a fight; he hoped to get some during his next tour of duty.
Meaning of duty for the defined word.
Grammatically, this word "duty" is a noun, more specifically, a countable noun.