Rule reminder
Italian impersonals of necessity exist on a register scale from informal to very formal: bisogna (neutral/colloquial) → occorre (formal) → è necessario (formal/written) → si richiede (official/bureaucratic) → è d'obbligo (mandatory/ceremonial). Choosing the right register is essential for written Italian at B2 level.
You are writing an informal message to a classmate. Which is most appropriate for 'we need to study more'?