1.   A Decade ago this was Checkpoint Charlie, one of the few gaps in an otherwise impenetrable barrier a hundred miles long.

2.   But this normally impenetrable barrier is easily breached by fat-soluble ethanol molecules, which slip through like little ghosts.

3.   Yet some people seem to learn to live with imperfection and others find it an impenetrable barrier.

4.   ...the Caucasus range, an almost impenetrable barrier between Europe and Asia.

5.   And the movie shows you exactly how that attitude and the expectations that go with it can act as an impenetrable barrier to any real personal fulfillment.

6.   Bumper-to-bumper buses ringed the White House to form an impenetrable barrier.

7.   For the deeply sensitive Cendrars, Hollywood was a walled city, each studio surrounded by an impenetrable barrier.

8.   For those who treasure the breaking of supposedly impenetrable barriers, Roger Bannister will always be a hero.

9.   It seemed an impenetrable psychological barrier.

10.   The ice can go no farther, but it remains as an impenetrable barrier to additional meltwater.