THE EFFECT OF LEARNING TOGETHER TECNIQUE ON THE ACHIEVEMENT OF WRITTEN EXPRESSION PEDAGOGICAL CONTENT KNOWLEDGE OF PROSPECTIVE PRIMARY EDUCATION TEACHERS/BİRLİKTE ÖĞRENME TEKNİĞİNİN SINIF ÖĞRETMENİ ADAYLARININ YAZILI ANLATIM ALAN BİLGİSİ BAŞARILARINA ETKİSİ