Problem: Nurse Emily is assessing Jacob, a 6-month-old male who presents with persistent vomiting, diarrhea, and signs of dehydration. His mother reports that he has not been gaining weight and has been irritable. His physical examination shows sunken fontanelles and dry mucous membranes. What is the most likely diagnosis for Jacob, and what diagnostic studies should be conducted to confirm this? A. O Gastroesophageal Reflux Disease (GERD); Perform an upper GI series B. O Pyloric Stenosis; Conduct an abdominal ultrasound C. O Rotavirus Infection; Obtain a stool sample for rotavirus antigen test D. O Cow's Milk Protein Allergy; Perform an elimination