This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Pharmacology
[{'content': 'Digoxin act on the heart by:(1994) \nSelect and explain. \nA. Decreasing preload, B. Increasing the force of contraction, C. Decreasing the afterload, D. Decreasing heart rate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: b.Ref: KDT, 5,h ed, p. 465, 457-458 & 4th ed, p. 494', 'role': 'assistant'}]