A futuristic, robot-like species has been observing the human race for thousands of years and has decided to remove them all from planet Earth. In what way could they do this, whilst also having the method they use allow three people to be left behind?
Okay, hopefully by providing a bit more context, there will be a few more answers. This alien race is, as I said, robot-like. They have actually been designed and created by another alien species, which the robots believe to have gone extinct. This supposedly extinct alien species believed that it has created the human race millions of years ago as an experiment, and sent the robots to remove the humans and allow life on the planet to continue without them. It has taken the robots an extremely long time to arrive at Earth.
Rather than simply murder them, the robots have been designed to feel compassion and emotion. As such, they decide to transport the humans onto an assortment of ships near Earth, and induce every one into a sleep-like coma, where they dream until their body withers away. The humans are kept in holding pens until the robots construct enough of these dream machines, hooking humans up to it in groups.
So the only thing I'm really interested in is how they get all the humans from point A to point B. I'm willing to accept an scenario where the three remaining humans are left behind on purpose, but really I'm after a way in which the robots could pull off this mass transportation.