The system described appears to be under repressible control. The Option B is correct.
In this context, the information provided suggests that the eryD gene product is involved in repressing a promoter site. This implies that under normal conditions, the gene's expression is actively repressed, likely to prevent the production of a specific product or function.
But when erythritol which is an external factor interrupts the action of the eryD repressor, it suggests that the system can be relieved from its repressed state and allowed to function.
This interruption leads to the induction of the system which is consistent with a repressible regulatory mechanism where the default state is repression and it can be temporarily lifted when needed.
The full question is:
The product of the eryD gene is probably involved in repressing a promoter site. The system is induced when erythritol interrupts the action of the eryD repressor.
Does this system appear to be under inducible or repressible control?
A. these data are consistent with an inducible system of regulation.
B. these data are consistent with a repressible system of regulation.
C. the type of control can not be determined from these data.