Hmm..

this kind of question is alarming, because it shows me you are probably not listening to the lectures

or at least, not focusing on the material, so not a lot of it is sticking with you.

these are important basic concepts that I explain numerous times, extensively, during the lecture, 

so make sure you review this section one more time before the exam, okay?

S phase is part of interphase, the cell cycle excluding the M phase.

S phase is where DNA synthesis occurs.

Mitosis is the division of the cell.

DNA replication does not occur during mitosis.

To put it in another way, all DNA must be replicated before the cell can divide.

Hope this helps :D