Hubungan Pengetahuan, Sikap, dan Perilaku Terhadap Talasemia, Hb Pre-transfusi, dan Kadar Serum Feritin pada Pasien Remaja dengan Talasemia = Association between Knowledge, Attitude, and Practice about Thalassemia, Pre-transfusion Hb, and Serum Ferritin Level among Adolescent Patients with Thalassemia