Does your state allow 2 people to DBA the same business? I read your message as meaning that your Section A states both their names somehow (John Doe and Jane Doe) and in the DBA field, it states "Farming Services." If you have 2 people (John and Jane) in the section A field, I would play it safe and indicate which of those 2 people conducted the transaction rather than checking "conducted on own behalf."
If, however, you have one section A on Jane Doe and one section A on John Doe DBA Farming Services, you could leave all section Bs blank by making the conductor appear in Section A on page 1 and then checking "conducted on own behalf" on page 1.
"It is natural to give a clear view of the world after accepting the idea that it must be clear." - Albert Camus