Air quality in Boston is generally very good: during the ten-year period 2004–2013, there were only 4 days in which the air was unhealthy for the general public, according to the EPA.
Air quality in Boston is generally very good : during the ten - year period 2004–2013 , there were only 4 days in which the air was unhealthy for the general public , according to the EPA .
How many days between 2004 and 2013 was the air unhealthy?
How many days between 2004 and 2013 was the air unhealthy ?
4 days
4 days