Yourself and eight graduate students are exploring a temple when you knock into an artefact, which causes the collapse of the ruins.

You're fleeing the falling rubble but come to a junction, with four possible exits, each of which will take 20 minutes to explore and then 20 minutes to return to alert the others as to whether it is the way out.

You have one hour to all get out safely.

However, the artefact has also possessed two people, who will now lie to attempt to trap you all in the temple forever.

You do not know which people, but you do know for certain that you are not possessed.

So how do you pick the safe way out?