A forecasting method has produced the following over the past five months. What is the mean absolute deviation $($MAD$)?$

$\backslash$table$[[$Actual$,$Forecast,Error,$||$ Error$|],[10,11,-1,1],[8,10,-2,2],[10,8,2,2],[6,6,0,0],[9,8,1,1]]$

a$.-0\mathrm{.}2$

b$.-1\mathrm{.}0$

c$.0\mathrm{.}0$

d$.1\mathrm{.}2$

e$.8\mathrm{.}6$