Correct Answer & Explanation
Option B
• The phrase 'when I was at school' clearly indicates a specific point or period in the past.
• For an action completed in the past at a definite time, the Simple Past Tense (V2) is used.
• 'Knew' is the simple past form of 'know'.
• 'Have known' (Present Perfect) is used for actions that started in the past and continue to the present or have an effect on the present, which is not the case here.
• 'Had known' (Past Perfect) is used for an action that occurred before another past action.
• 'Am knowing' is incorrect as 'know' is a stative verb and generally not used in continuous tenses.