名词
中文翻译：索引
同义词：
['mark', 'key', 'reference point']
例句：
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1. The index of the stock market has been rising steadily for the past week.
过去一周，股市的指数一直在稳步上升。
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2. The index of the economy is closely watched by economists around the world.
全世界的经济学家都密切关注着经济指数。
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3. The index of happiness is a measure of how happy people feel in their daily lives.
幸福指数是衡量人们日常生活中幸福感的一种方式。