In which year, the absolute difference of the students in two schools is the lowest ?

From the bar graph,

The absolute difference of the students in two schools in 2008 = $$\left|640-550\right|=90$$

The absolute difference of the students in two schools in 2009 = $$\left|800-820\right|=20$$

The absolute difference of the students in two schools in 2011 = $$\left|700-750\right|=50$$

The absolute difference of the students in two schools in 2012 = $$\left|900-500\right|=400$$

$$\therefore\ $$The absolute difference of the students in two schools in 2009 is the lowest

Hence, the correct answer is Option A