11.   The researchers at the Roslin Institute in Scotland achieved what many had thought biologically impossible.

12.   The Slide Brook quad whizzes riders through a mile of Vermont wilderness over a deep chasm that was once thought impossible to bridge.

13.   The two are separated by a deep chasm that, over the decades, was thought impossible to bridge.

14.   The younger man, Adolph Simon Ochs, was making a career of doing things other people thought impossible.

15.   They show clearly and unmistakably what so many experts had once thought impossible.

16.   In a field few have delved in, the Kher brothers are aspiring towards a dream they once thought impossible.

17.   In the two weeks he has been president, he has brought changes once thought impossible in this vast archipelago.

18.   The truth is that Coutis can do what most conscious minds think impossible.

19.   They have seemingly managed to make possible what was once thought impossible.

20.   Thinking it impossible, he tried to dismiss the notion, but it had already taken root in his mind.