$A$ box of mass $2 kg$ is placed on the roof of a car. The box would remain stationary until the car attains a maximum acceleration. The coefficient of static friction between the box and the roof of the car is $0.2$ and $g=10 ms^{-2}$. This maximum acceleration of the car, for the box to remain stationary, is: (in $ms^{-2}$)

• A
  $8$
• B
  $6$
• C
  $4$
• D
  $2$