Vitamin K antagonizes
(A) Corticosteroids (B) Thrombin formation (C) Bishydroxy coumarin (D) Production of clotting factors by liver
(C) Bishydroxy coumarin (dicoumarol), a vitamin K antagonist may be considered as an oral anticoagulant. 
This acts by reducing  the synthesis of certain clotting factors (ll, Vll, lX and X).

Ref : Lippincott’s illustrated reviews for biochemistry , 7th edition.