classes:  lecturer. difficult to understand subjects, finished studying just visualize a little about the subject, the teacher has not yet understood the subject.  curriculum. difficult to understand subjects, finished studying just visualize a little about the subject, the teacher has not yet understood the subject.  facility. difficult to understand subjects, finished studying just visualize a little about the subject, the teacher has not yet understood the subject.  general. difficult to understand subjects, finished studying just visualize a little about the subject, the teacher has not yet understood the subject.