professionalize(в какой-либо профессии); specialize(with в + prepl. or по, in; usually with in; go give one's attention (to), work (in), or study (a particular job, subject etc.) • He specializes in fixing computers); enter on a career(в какой-либо сфере); stake out the market(на чем-то tavost); make a speciality(в чём-либо-of); concentrate(on); give specialized training; specialise(usually with in; go give one's attention (to), work (in), or study (a particular job, subject etc.) • He specializes in fixing computers); focus(на деятельности предприятия и т.п.); bias(DariaChernova); active in(в/на чём-либо Post Scriptum); major(with in; American; to study a certain subject in which you specialize at college or university • She is majoring in philosophy)
specialize(in, в рамках выбранной специальности); major(in ... – на ... чём-л. • I major in elementary education and minor in psychology.Alex_Odeychuk)