The child’s arm was swollen because he __________ by a bee. stung had

The child’s arm was swollen because he __________ by a bee.

• A. stung
• B. had stung
• C. had been stung
• D. had being stung

was swollen (kết quả trong quá khứ) 

=> dùng quá khứ hoàn thành (nguyên nhân của hành động/vấn đề trong quá khứ)