The question is about selecting the correct tense for a past action. 'B. Past Continuous' is used to describe an action that was ongoing at a particular moment in the past, which is the direct basis for choosing this option. 'A. Present Perfect' refers to an action that has happened at an unspecified time in the past, 'C. Future Perfect' is for an action that will be completed by a certain time in the future, and 'D. Present Simple' is for general facts or habits. These tenses do not describe an action at a specific moment in the past.