A 25-year-old man presented with abdominal pain which started two days ago. Yesterday, the pain was periodic and located around the periumbilical area. Today, the pain is persistent and localized in the right lower abdomen.
His body temperature is 37.7℃, pulse rate 90/min, blood pressure 120/62 mmHg, and respiratory rate 16/min. Physical examination shows rebound tenderness at the right lower abdomen.
Which one of the following should be performed next？

1. Abdominal CT
2. Central venous (CV) catheterization
3. Gastrointestinal endoscopy
4. Magnetic resonance cholangiopancreatography (MRCP)
5. Nasogastric tube insertion