Which of the Following Entities Is Eligible to Establish a Keogh

Which of the following entities is eligible to establish a Keogh Plan?

A) Ms. Dee Ziner is the owner of an interior design company that is established as a sole proprietorship.
B) Mr. Hans Deutsch is the owner of a Subchapter S Corporation that imports only Bavarian-made goods.
C) Mr. Will Writer teaches English at a community college and does freelance writing to supplement his income.
D) Both A and C are eligible to establish a Keogh Plan.