Given the following window class, what type of variable is count?

class Demo$($EasyFrame$)$:

$$ def $\_\_$init$\_\_($self$)$:

$"""$Sets up the window and widgets."""

$$ EasyFrame.$\_\_$init$\_\_($self$,$ title $=$ "Demo", width $=600)$

$$ self.addLabel$($text $="$An integer", row $=0,$ column $=0)$

$$ self.inputField $=$ self.addFloatField$($value $=0\mathrm{.}0,$row $=0,$ column $=1)$

$$ self.addLabel$($text $=$ "Square root", row $=1,$ column $=0)$

$$ self.outputField $=$ self.addFloatField$($value $=0\mathrm{.}0,$ row $=1,$ column $=1,$ precision $=3,$ state $=$ "readonly"$)$

$$ self.addButton$($text $=$ "Compute", row $=2,$ column $=0,$ columnspan $=2,$ command $=$ self.computeSqrt$)$

$$ self.count $=0$

$$ def computeSqrt$($self$)$:

$$ number $=$ self.inputField.getNumber$()$

$$ result $=$ math.sqrt$($number$)$

$$ self.outputField.setNumber$($result$)$

$$ self.count $+=1$

Question $26$ options:

a$)$

constant variable

b$)$

instance variable

c$)$

string variable

d$)$

local variable