Rule reminder
'Prima che' (before) always requires the subjunctive. Other temporal conjunctions like 'dopo che' (after) and 'quando' (when) normally use the indicative, but 'prima che' is unique because the action it refers to has not yet occurred at the time of the main action — making it inherently uncertain.
They sold the shares before the market crashed. Choose the correct form: 'Hanno venduto le azioni prima che il mercato _____.'