Which of the following statements about the regulation of the lac operon is true?
(a) When glucose is present, gene expression is activated by lactose
(b) The amount of glucose in the growth medium does not affect the level of gene expression activated by lactose
(c) The binding of the lac repressor to the operator is not affected by the presence of glucose
(d) Gene expression is high when the lac repressor is not bound to the operator and glucose is available.