A 68-year-old white man comes to the clinic complaining of fatigue and shortness of breath. Physical examination reveals a palpable liver edge 3 cm below the right costal margin and a 2+ pitting edema of the lower extremities. You notice in his clinic chart that he initially presented 2 months earlier complaining of a 4-month history of shortness of breath that was worse on exertion and caused him to routinely awaken from sleep to go to the window to "get air". You see that at that time in the chart it says that the "cardiac examination is unremarkable and there is no jugular venous distension or pitting edema. However, there are fine bibasilar crackles". You can see that the patient was prescribed a medication, but unfortunately you cannot read what it was and of course he did not bring the bottle with him. At this time, the most likely underlying cause of this patient's condition is A. asthma B. biventricular heart failure C. cor pulmonale D. left heart failure E. right heart failure