In a university database, if there is an entity for "Professor" $($E$1)$ and "Course" $($E$3),$ what relationship type might exist between Professor and Course?

a$.$ N$-1($Many$-$to$-$One$)$

b$.1-N($One$-$to$-$Many$)$

c$.,N-M($Many$-$to$-$Many$)$

d$.1-1($One$-$to$-$One$)$