21. In E. coli glucose represses the gene expression of many sugar utilization genes (ie lactose operon). Which of the following statements is/are correct? I. The glucose effect is mediated by the operator site of the lactose operon. II. The glucose effect is mediated by the lactose repressor. III. The glucose effect is mediated by a negative regulation. IV. The glucose effect is mediated by the concentration of cAMP. (A) III (B) IV (C) I and II (D) III and IV (E) I, II and III