The answer is D. Lecturer.
A teacher is a person who helps others learn. They can be found in schools, colleges, and universities. Principals are the leaders of schools. They are responsible for the day-to-day running of the school and for making sure that students are learning. Students are the people who attend school. They learn from their teachers and take exams to show what they have learned. Lecturers are people who give lectures at universities. They are experts in their field and share their knowledge with students.
The word “lecturer” is different from the rest because it is the only word that refers to someone who gives lectures. The other words all refer to people who are involved in education, but they do not necessarily give lectures.