Acylindrical blood vessel is partially blocked by the buildup of plaque. at one point, the plaque decreases the diameter of the vessel by 60%. the blood approaching the blocked portion has speed v0. 1) just as the blood enters the blocked portion of the vessel, the blood's velocity will

 It will slow down.

Explanation:  This is because the same amount of blood that usually goes through will have to fit through a blocked vessel.  Only a little will be able to go through at one time, causing the blood flow on the other side to slow.

(That is really dangerous.  The build-up will eventually burst the vessel)  Just an FYI