A 7-year-old boy with cystic fibrosis presents to the clinic with recurrent nosebleeds and easy bruising over the past month. His parents report he has chronic steatorrhea and has been noncompliant with his pancreatic enzyme supplements. On exam, there are multiple ecchymoses on his arms and legs and mild bleeding from his gums. Laboratory studies show a prolonged prothrombin time (PT), a slightly prolonged activated partial thromboplastin time (aPTT), and a normal bleeding time. Which of the following vitamins is most likely deficient in this patient?