A professor who always grades on a curve cannot finish scoring the midterm exams until all of the students have completed taking the test. What kind of relationship is this?

a$.$ Start$-$to$-$start $($SS$)$

b$.$ Start$-$to$-$finish $($SF$)$

c$.$ Finish$-$to$-$start $($FS$)$

d$.$ Finish$-$to$-$finish $($FF$)$