We would have helped you if we ... you were in trouble. Choose the correct option: knew; have known; had known.

Правильный вариант: had known.

Предложение: We would have helped you if we had known you were in trouble. — «Мы бы помогли вам, если бы знали, что вы попали в беду». Условие относится к нереальной ситуации в прошлом, поэтому используется Third Conditional: would have + причастие в главной части и Past Perfect в придаточной.

Ответ: had known.