Eagle has been flying in the sky . . . . . last week. A. since B. for C. over D. before

The answer is since.

• Since is used to indicate the beginning of an event or action. In this case, the eagle has been flying in the sky since last week.
• For is used to indicate the duration of an event or action. In this case, the eagle has been flying in the sky for a week.
• Over is used to indicate a distance or a period of time. In this case, the eagle has been flying over the sky.
• Before is used to indicate a time that is earlier than a particular point in time. In this case, the eagle was not flying in the sky before last week.