Final answer:
A constitutive operon is one that is continuously transcribed and translated, providing steady protein levels without being regulated by external or internal signals.
Step-by-step explanation:
The correct answer to the question is C. constitutive. An operon that continuously transcribes and translates its genes to provide consistent levels of protein products is known as a constitutive operon. Unlike repressible or inducible operons that respond to environmental or cellular signals, constitutive operons are not subject to regulation and thus encode proteins at a constant rate.