In an experiment, biologic characteristics of neoplastic and non-neoplastic cells are analyzed in culture. The biochemical expes repo that it is observed that cell division in cells derived from malignant neoplasms, but not in normal cells, is aided by the presence of an enzyme which repairs progressive chromosomal shoening. The lack of chromosomal shoening allows the malignant cells to undergo many more divisions than the normal cells. Which of the following enzymes is most likely to have this effect?