The Reason That the Textbook Converted the Basic Production Function

The reason that the textbook converted the basic production function as specified by Robert Solow, Y = F(K,L) to the form y = f(k) , where y and k represent Y/L and K/L, respectively, is that:

A) this representation of the production function matches our definition of economic growth as the change in per capita output.
B) this form is easier to write because there is only one factor, rather than two, in the production funtion.
C) this form is closer to the production function suggested by Adam Smith.
D) this form uses lower case letters, which are less confusing.