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You are in a tower at a rail yard where you can control one switch. A train is approaching the fork in the tracks with that switch. (You cannot leave the tower or call anyone until the train passes.)
On one track, a person is tied to the rails. The other track is damaged. If you do nothing, the train will continue onto the damaged track and derail. Many of the passengers and crew will be killed as a result. If you switch the train onto the other track, it will pass safely onto its destination, but it will kill the person tied to the tracks.
It's your decision . . .