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: Unknown
Hardness of water occurs due to the presence of all of the following except: 
Select and explain. 
A. Calcium bicarbonate, B. Magnesium bicarbonate, C. Calcium sulfate, D. Magenesium Oxide
D: Magenesium Oxide
Answer: D: Magenesium Oxide 
Explanation: Ref. Foundations of Community medicine. Page. 46
 
Hardness of water:

Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate).  
Permanent hardness is caused by dissolved calcium sulfate (which is not removed by boiling).