In a university, the data of students such as student id$,$ name, and address are recorded in the STUDENT table and the courses are stored in a COURSE table by the course code, number of credits, and professor teaching. Usually, a student takes up to five courses per cycle, and each course has a minimum of two students. What kind of relationship exists between the courses and students?

a$.$ Functional dependence

b$.1$:M

c$.M$:$N$

d$.1$:$1$