Answer:
Labeled ddNTPs
Explanation:
The chain termination method or sanger method consist in 4 synthetis reaction at the same time. Each of them with a different labeled ddNTPs (ddATP, ddCTP, ddGTP and ddTTP) as part of it sythesis sustract. As the reaction goes on, if a ddNTP is added to the new DNA chain, it will stop the elongation becouse DNA polymerase activity depends on the presence of -OH extremes which are miss on ddNTPs.
