This is 16th century 3 part 3rd and 4th species fusion counterpoint.
At the second measure, there's C, The first note on the soprano.
In the bass, there's sustained D, which will resolve to C.
The problem is, my book said: The to be resolved note should not appear in any other parts ( Soprano's C ).
I believe there is some exception to that rule going on here..but I don't know.
I will really appreciated if somebody could help me what's going on here.
( The Alto part is on Alto clef..just in case anybody is confused )