Components of blood

A patient is given a drug that reduces the activity of vitamin K in the body. Vitamin K is needed for the synthesis of prothrombin. What is the most likely effect of this drug on blood clotting?

A) Blood clots form faster because more thrombin is produced
B) Blood clots form slower because less prothrombin is produced
C) Blood clots form faster because more fibrinogen is produced
D) Blood clotting is unchanged because vitamin K is not involved