The main purpose of the author is to convince the readers to D. spend as much time developing the mind as developing the body.
It should be noted that purpose is the theme in the story. It contains the underlying message.
In this case, the main purpose of the author is to convince the readers to spend as much time developing the mind as developing the body.
Learn more about purpose on:
https://brainly.com/question/11827791
#SPJ5