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: Surgery
Cardiac glycosides are obtained from following plant source: 
Select and explain. 
A. Rauwolfia serpentina., B. Strophanthus gratus., C. Ricinus communis., D. Atropa belladonna.
B: Strophanthus gratus.
Answer: B: Strophanthus gratus. 
Explanation: The following are obtained from Rauwolfia serpentina--Reserpine. Strophanthus gratus--Strophanthin-G (Ouabain) A cardiac glycoside. Ricinus communis--Castor oil. Atropa belladonna--Atropine