I know this is a very basic necessary/sufficient question but could someone validate the way I diagramed the logic?

Stim:

Professor: both O parents --> only O child

Student: not [both O parents --> only O child], but the student switched the professor's statement around to mean [only O child --> both O parents]. So given his logic, /both O parents --> /only O child (since he's Type B).

ACs:

A) only O child --> both O parents

B) both O parents --> /type B child

C) both B parents --> only O children

D) irrelevant

E) both B parents --> type B children

#help