Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: The initial procedure of choice to investigate a possible obstruction of the biliary tract is: 
 Options:  <1> Hepatobiliary ultrasound. <2> Endoscopic retrograde cholangiopancreatography (ERCP). <3> Colangio Magnetic Resonance. <4> Computed tomography. Abdominal CT <5> Percutaneous transhepatic cholangiography.
