index of places

例句：

1. 1. The index of the stock market has been rising steadily since the beginning of the year.
   自年初以来，股市的指数一直在稳步上升。
2. 2. The index of the economy is closely watched by economists around the world.
   经济指数是全世界经济学家密切关注的指标。
3. 3. The index of happiness is a measure of how people feel about their lives.
   幸福指数是一个衡量人们对自己生活感受的指标。