Where does a restriction enzyme cut DNA?

Correct answer: At a specific recognition site

Restriction enzymes are sequence-specific endonucleases, which is the governing concept here. Each enzyme recognizes a short DNA sequence called its recognition site, often a palindromic sequence, and cleaves the phosphodiester backbone at a defined position within or close to that site. This predictable cutting is why the enzymes are useful for making recombinant DNA fragments. Option B is therefore correct. The enzyme does not target a protein region, a cell membrane, or a ribosome: those choices describe structures or molecules outside the DNA substrate used in the digestion reaction.