第6题: [单项选择]Although he was under no {{U}}obligation{{/U}} the shopkeeper replaced the defective battery free of charge. A. guarantee B. duty C. power D. authority 参考答案:B 答案解析:to be under obligation“有责任,有义务”。选项中只有B.duty有“责任”之意,与之意思相近。guarantee“保证”;power“能力”;authority“权威,权力”。