John Maynard Keynes Described Economics as an Easy Subject at Which

John Maynard Keynes described economics as an easy subject at which very few excel.Which of the following is not one of the reasons Keynes gave for why so few people excel at the study of economics?

A) An economist must also be a mathematician,historian,statesman,and philosopher in some degree.
B) An economist must understand symbols and speak in words.
C) An economist must be purposeful and disinterested in a simultaneous mood.
D) An economist must understand environmental science,regulation,and political science.