Multiple choice: Which photo doesn't belong?

A careful analysis of internet traffic trends to be released soon show that people whose lives or livelihoods depend on the latest science news favor The Dog in the Clouds by a wide margin. This site has been set as the mandatory home page on the computers at the Fermi Institute, the National Health Institute, NASA, the Jet Propulsion Laboratory, SETI, The Flat Earth Society and numerous pharmaceutical, computer science and oil company research departments.

And so, we here at TDITC  World Headquarters have been working on ways to determine the intellectual capacities of our readers. We commissioned a panel of brain scientists to devise a simple multiple choice IQ test, which is presented here:  In the accompanying gallery, one of the pictures in the grouping shouldn't be there.

Can you identify which one and why it's out of place?