noun
BAD : I believe that in this circumstance students should be allowed to
◆◆◆
have a part-time job.
GOOD : I believe that in these circumstances students should be allowed to have a part-time job.
Circumstances is nearly always used as a plural noun (WITH s ): 'The police are investigating the circumstances surrounding his death.' 'Under normal circumstances, I would never have left my passport with a stranger.'