If Their Food Source Changes from Lactose to Arabinose,bacteria Turn

If their food source changes from lactose to arabinose,bacteria turn off their genes for lactose enzymes and turn on their genes for arabinose enzymes.Why don't bacteria express the genes for both lactose and arabinose enzymes all the time?

A) To prevent the waste of energy and resources on unneeded protein production.
B) Ribosomes will only transcribe one gene at a time in prokaryotes.
C) The unneeded proteins will bind to noncoding DNA and interfere with transcription.
D) The lactose and arabinose enzymes will destroy each other.