Why Might a Professor Asking a Student for a Date

Why might a professor asking a student for a date be considered harassment?

A) The professor is older and more educated than the student.
B) The professor's power over the student (i.e. ,grading) limits the student's ability to accept or refuse freely.
C) The student can spread false rumors about the professor and ruin his/her reputation among colleagues.
D) The student can gain power over other students because of his/her special relationship with the professor.