题目

Every day, on her way to work, Amelia had to pass a slum(贫民窟). As 16 social worker, she had not paid much attention to 17 . This changed one day when she met a ragged boy named Sam. Sam knew 18 she was the head of social services, and that she could help. He reached out his hand 19 said, “Can you help me? I’m looking for my dad.” His hands were so cold. Amelia said, “What’s up?” “My mom is 20 (terrible) sick. Her birthday is coming. I know my father’s coming back would be the best present. My dad had left us 21 I was two years old,” said the boy. Ameli某物质R与水和氧气发生的化学反应为：2R+2H2O+7O2=2FeSO4+2H2SO4则R的化学式是（　　）A．FeSB．Fe2S3C．FeOD．FeS2