Scientists estimate that smoking reduces life expectancy by around 2 years on average.

科学家们估计，吸烟使预期寿命平均缩短了大约两年时间。

The average life expectancy was 40.

平均期望寿命曾是40岁。

Life expectancy is about 60 years.

寿命约在60岁左右。

One of my favorite metrics is life expectancy.

我喜欢的一个指标是平均寿命。

Health is poor and life expectancy is low.

卫生糟糕，寿命预期值低下。