A patient is receiving heparin therapy as part of the treatment for a pulmonary embolism. The nurse monitors the results of which laboratory test to check the drug's effectiveness?

A. (PT/INR) is used to monitor warfarin, not heparin. B. Vitamin K is not monitored for heparin. C. Bleeding times are too nonspecific for therapeutic monitoring. D. aPTT measures the effectiveness of heparin therapy and how well it is prolonging clotting time.