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.
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