19. Which of the following statements about regulation of the lac operon is true? (A) In the presence of lactose, the lac repressor, lacl, halts production of the enzymes encoded by the lac operon. (B) The gene product of lacZ is ẞ-galactosidase which cleaves lactose into glucose and galactose. (C) Glucose in the growth medium does not affect the inducibility by lactose. (D) Glucose in the growth medium increases the inducibility by lactose. (E) Its expression is regulated mainly at the level of translation.