What is the benefit if a DNA fragment and vector are cut with the same restriction enzyme?

Correct answer: Complementary ends form and joining becomes easier

The correct answer is A: complementary ends form, so joining becomes easier. A restriction enzyme cuts DNA at a particular recognition sequence. When the DNA fragment and vector are cut with the same enzyme, their exposed single-stranded ends are usually compatible, often called sticky ends. The matching bases can pair by hydrogen bonds, and DNA ligase can seal the remaining breaks to make recombinant DNA. Option A is correct because matching ends bring the two DNA pieces together in the proper construction step. Option B is wrong because restriction enzymes cut DNA at specific sites; they do not always destroy both molecules. Option C is wrong because cutting DNA does not always stop protein formation; the result depends on the gene and cell. Option D is wrong because the DNA molecule does not change colour merely because it was cut. Memory cue: same cutter, compatible ends, easier joining.