This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Patient is on Cisapride for gastroesophageal reflux develops upper respiratory tract infection, and physician prescribes erythromycin. What pharmalogical interaction would be expected - 
Select and explain. 
A. Dereased level of erythromycin and exacerbation of UI, B. Decreased effect of cisapride due to enzyme inductor of erythromycin, C. Fatal ventricular arrhythmia, D. Hemorrhagic cystitis
C: Fatal ventricular arrhythmia
Answer: C: Fatal ventricular arrhythmia 
Explanation: Ans. is 'c' i.e., Fatal ventricular arrythmia