The correct answer is choice A. Factor II, also known as prothrombin, is one of the coagulation factors that are activated by vitamin K. Vitamin K is a cofactor for the carboxylation of specific glutamic acid groups in coagulation factors II, VII, IX, and X.

This process is essential for the activation of these factors in the coagulation cascade.

Choice B is wrong because factor V is not a vitamin K-dependent coagulation factor.

Factor V is activated by thrombin and acts as a cofactor for factor Xa in the conversion of prothrombin to thrombin.

Choice C is wrong because factor VIII is not a vitamin K-dependent coagulation factor.

Factor VIII is activated by thrombin and acts as a cofactor for factor IXa in the activation of factor X.

Choice D is wrong because factor XI is not a vitamin K-dependent coagulation factor.

Factor XI is activated by factor XIIa and activates factor IX in the intrinsic pathway of coagulation.

Normal ranges for coagulation factors are:

• Factor II: 70-120% of normal activity

• Factor V: 50-150% of normal activity

• Factor VIII: 50-150% of normal activity

• Factor IX: 50-150% of normal activity

• Factor X: 70-140% of normal activity

• Factor XI: 70-150% of normal activity