Sir David Nicholson has signed a wall at an NHS conference to "pledge to become a dementia friend," someone who is trained to help spot the early signs of the disease.
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Karl, 17, was stabbed to death when his friends became involved in a row with around a gang of youths in Hackney, east London in 2004.
Researchers believe they have found the wreckage of British explorer James Cook's ship "Endeavour".
Four kittens have been rescued from a fire by emergency services in California, USA.