Gnu:
Yup. And there are two doors available. ONE choice between TWO doors (options). The fact that there were three doors at the start simply cannot influence ONE choice between TWO options in the second round.

Yes, you have a choice between two doors, but not two identical doors.

What differentiates them?
A) On has a car behind it the other has a goat.
Unfortunately, we cannot know for sure which is which (yet)
B) One of the doors was selected earlier, at which time we knew there was only a one in three chance of it being the one with the car.

If Monty had left you with a choice of three doors (the one he has shown to contain a goat is not removed) how would you decide?
Your choice is still 1/3 now, so does the car still have an equal chance of being behind each door?
Your previously chosen door still has a 1/3 chance of hiding the car.
You know that the door Monty opened has a 0% chance.
Is the chance if you switch 1/3 (the same as your chosen door)?
If so you have three options which only add up to 2/3.

Should the odds on both the remaining doors have increased, or has Monty given you enough information to increase the likelihood that the unchosen door hides the car?