The correct answer is $\boxed{\text{B) 3 sec}}$.
The formula for calculating the stopping distance of a car is $d = \frac{v^2}{2\mu g}$, where $d$ is the stopping distance, $v$ is the initial velocity, $\mu$ is the coefficient of friction, and $g$ is the acceleration due to gravity.
In this case, $v = 20 \text{ m/s}$, $\mu = 0.8$, and $g = 9.8 \text{ m/s}^2$. Substituting these values into the formula, we get $d = \frac{(20 \text{ m/s})^2}{2(0.8)(9.8 \text{ m/s}^2)} = 40 \text{ m}$.
Therefore, the car will take 3 seconds to stop.
Option A is incorrect because the stopping distance is 40 meters, not 20 meters. Option C is incorrect because the stopping distance is 40 meters, not 60 meters. Option D is incorrect because the stopping distance is 40 meters, not 80 meters.