Answer
b) is correct.
Work Step by Step
We have $$\overline F=\frac{J}{\Delta t}=\frac{|p_f-p_0|}{\Delta t}$$
Region A: $\overline F_A=\frac{|8-4|}{4}=1N$
Region B: $\overline F_B=\frac{|8-8|}{1}=0$
Region C: $\overline F_C=\frac{|0-8|}{2}=4N$
Region D: $\overline F_D=\frac{|0-0|}{2}=0$
So, we find that the magnitude of the force in region C is the largest, and in region B and D it is the smallest. b) is correct.
