index of operating rates

例句：

1. 1. The index of the stock market has been rising steadily.
   股市的指数一直在稳步上升。
2. 2. The index of the economy is closely monitored by economists.
   经济学家密切监控着经济指数。
3. 3. The index of happiness is a measure of how people feel about life.
   幸福指数是衡量人们对生活感受的一个指标。