She has been working here ______ five years.

• A. Since
• B. During
• C. For
• D. Over

Answer: (C)

This sentence uses a present perfect continuous structure to show an action that started in the past and continues now, and it needs a duration expression. When you want to say how long something has been happening, you use for plus a length of time. For five years means the action has been ongoing for that entire span up to the present.

Since would require a starting point in time (since 2011, since I started, etc.), not just a length of time. During is used with a noun phrase for a period (during the past five years), but the bare five years doesn’t fit smoothly after the verb here. Over can work in similar ideas like “for over five years” or “over the past five years,” but the sentence as written needs for to be natural and correct.