💡 Detailed Explanation
The grammar pattern '〜ものだから' is used to give a reason or make an excuse. '〜てしまう' adds the nuance of something happening unintentionally. To make the sentence mean 'I couldn't answer well because I got extremely nervous during the interview,' the correct order is 「して」「しまった」「ものだから」「うまく」. The word that goes in the star (★) position is the third one, 「ものだから」.