Answer:
 vâ = 2 vâ  blood velocity in the built zone is twice the speed of the normal zone,  so the correct response is c
Explanation:
For that problem we must use the fluid continuity equation
     Aâ vâ = Aâ vâ
Where point 1 is in the normal artery and point 2 in the contraction
     vâ = vâ  Aâ / Aâ
In the exercise indicates
     Aâ = ½ Aâ
     vâ = 2 vâ
The blood velocity in the built zone is twice the speed of the normal zone, so the correct response is c