21. In E. coli cells, when lactose is absent from the environment,
(A) large amounts of b-galactosidase, lactose permease, and galactosidetransacetylase are made.
(B) trace amounts of b-galactosidase, lactose permease, and galactosidetransacetylase are made.
(C) no b-galactosidase, lactose permease, andgalactosidetransacetylas are made.
(D) the lac operon is induced.

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