Which of the following statement(s) concerning laboratory studies used in monitoring a patient with intravenous heparinization is/are correct? a. The platelet count should be followed because of the risk of heparin-associated thrombocytopenia b. The prothrombin time should be observed if prolonged treatment is necessary c. The activated partial thromboplastin time (aPTT) should be maintained at approximately 1.5 times normal d. The serum creatinine should be measured daily to allow adjustments in dose based on renal function