If these were the choices:
A. It's impossible to keep personal and work roles separate. B. Romance between a worker and a supervisor must always be out of bounds.
C. The price of a failed workplace romance may be your job.
D. Productivity and efficiency aren't affected by office romances.
I'd choose Choice B. Romance between a worker and a supervisor must always be out of bounds as the statement that is true. This is to avoid conflict of interest and collusion.
Choices A, C, and D are all dependent on how mature and committed the individuals in a relationship are. They can separate work and personal business. Productivity and efficiency need not be affected by office romances and your job must not be the price of a failed romance. These all depend on how you handle office romance and its consequences in the event of its failure.