You need to define 'correct'. (1) To a hidebound academic or wannabe, (a) as it avoids the Addisonian termination. (2) To a liberal grammarian, either. (3) To 98% of native speakers, (b), because (a) sounds rarefied. But if you're in academia, you'd better check the in-house style requirements.
– Edwin AshworthJan 19 '22 at 12:17
4
They are both grammatically correct, but semantically the first is considered more formal, while the second is more natural.
– BillJJan 19 '22 at 13:21