Restriction enzymes.....?

It is B as has been said, but the etymology is a little different. Restriction enzymes are bacterial in origin and are actual a defense mechanism. The enzymes evolved to cut DNA at specific sites common to parasitic viruses but innocuous to themselves. So they are produced by bacteria to "restrict" the infectivity of viruses in bacterial cells. The reason they're so handy is that scientists often need to produce recombinant DNA from multiple other pieces, so they can use restriction enzymes to get very precise cutting.