It was a mistake not to study. \u2192 You \_\_ have studied more.

Ответ (EN)

• It was a mistake not to study. → You should have studied more. (The modal verb 'should' is used to express that something was a good idea in the past but did not happen).

Перевод (RU)

• Было ошибкой не учиться. → Тебе следовало бы учиться больше.