Which one of the following hydrolyses internal phosphodiester bonds in a polynucleotide chain ?

Using imprints from a plate with complete medium and carrying bacterial colonies, you can select streptomycin resistant mutants and prove that such mutations do not originates as adaptation. These imprints need to be used -

Telomerase is an enzyme which is a -

E. coli cells with a mustard z gene of the lac operon cannot grow in medium containing only lactose as the source of energy because -