There are 3 doors.

A B C

One of them has a million dollars.

Let us assume you choose door A (without opening it yet) as the door with a million dollars.

After your selection, I inform you that the million dollars is NOT behind door B (and I open it to show you that it indeed is not there).

The question and puzzle is, if I were to give you the choice to switch to door C, would you? And if so, why? If you would not, why? Or does it not matter?