The correct answer for this question would be repressible enzymes.
Repressible enzymes are those which bind to the operator, and then block
the attachment of RNA polymerase, which therefore prevents the
transciption of genes. From this, we know that these are the types of
enzymes that are synthesized in an environment where an operon is needed
to code for enzymes that synthesize a protein from precursor amino acid
molecules.
