Astudent can attend five classes, each with a different professor. each professor has 30 students. the relationship of students to professors is a relationship.

Many-to-many relationship.

Explanation:

A many-to-many relationship occurs when multiple records in one table are associated with multiple records in another table. That is, an X element is related to many Y elements, while a Y element is related to many X elements. An example of this can be seen in the question above where a student can attend five classes, each with a different teacher. Each teacher has 30 students.

all cities have a governor

all cities are in states or provnies then country

all cities have people

difference

some are rich

some are poor

some are average