How can star activity be avoided?

Correct answer: Use recommended buffer and correct enzyme amount

The direct answer is A: use the recommended buffer and the correct amount of enzyme. Star activity means that a restriction enzyme loses its usual sequence specificity and cuts at sites that are similar to, but not exactly, its normal recognition site. Step by step, the enzyme needs the correct pH, salt concentration, temperature, reaction volume, and DNA-to-enzyme ratio. Therefore, use the manufacturer-recommended buffer, avoid adding excessive enzyme, do not incubate unnecessarily for too long, and keep the reaction conditions suitable. Option A is correct because these steps preserve accurate cutting. Option B is wrong because sunlight can damage or inactivate the enzyme. Option C is wrong because always boiling DNA can damage it and does not prevent star activity. Option D is wrong because salt must not simply be removed in every reaction; the correct salt concentration is needed, and excessive salt or unsuitable conditions are the real concerns. Exam cue: star activity usually points to non-ideal reaction conditions, excess enzyme, or excessive incubation.