An Operon Is Discovered That Produces A Constant Supply Of A Substance A Needed

An operon is discovered that produces a constant supply of a substance A needed by the body.  This operon would be:

a. constitutive but repressed when enough A was produced

b. inducible but repressed when enough A was produced

c. inducible, but enhanced when enough A was produced

d. repressed when not enough A is produced

e. enhanced when enough A is produced