As of 1975, the diseases which caused 2/3's of the deaths in the US included all but which of the following?

The correct answer is rooted in historical public health data and the epidemiological trends observed in the United States around 1975. At that time, the leading causes of death were significantly influenced by chronic diseases rather than infectious diseases. Heart disease, cancer, and cerebrovascular disease (stroke) were among the top causes of mortality, collectively accounting for a large proportion of deaths during this era.

Influenza, while it can contribute to mortality rates, especially in vulnerable populations during certain years, did not rank among the top causes of death in the context of the broader trends of chronic diseases that dominated health statistics at that time. Influenza-related deaths tend to spike in epidemic years but have not consistently been a primary contributor to overall mortality in the same way that chronic diseases have. This distinction emphasizes the shift in public health focus from infectious diseases to the management and prevention of chronic diseases over time.

Therefore, understanding the landscape of mortality statistics from that period highlights why influenza is the exception in this context. Chronic diseases characterized the burden of morbidity and mortality, illustrating the evolving nature of health concerns as the population aged and lifestyle factors contributed to increased incidences of these conditions.