The correct option is A Had remembered
Here, 'had remembered' in Past Perfect Tense is correct because it
is used to indicate a completed action of the past that happened before another
event took place.
'Remembered' in past simple is incorrect because
it indicates an action that has already been completed.
'Would remembered' is grammatically incorrect.
'Could remember' in present simple is incorrect because
it is used to indicate a future event on a designated date as part of a
plan or to express habits or general truth.