They understood that they....a mistakea)madeb)makec)had maded)are making

They understood that they had made a mistake.

Они сообразили, что сделали ошибку.

Did they understand that they had мейд a mistake?

Did the understand or forget that they мейд a mistake?

What did they understand?

What had they made?

Who understood that they had made a mistake?

Who had мейд a mistake?

They understood that they had mad a mistake, didnt they?