average molecular weight

例句：

1. 1. The average temperature in the city is around 20 degrees Celsius.
   这座城市的平均温度大约是20摄氏度。
2. 2. The average life expectancy for women in their 50s is around 83 years.
   50岁女性的平均预期寿命约为83年。
3. 3. The average income of a doctor is much higher than that of an engineer.
   医生的平均收入远高于工程师。