The new US Secretary of State John Kerry today recalled getting lost in London Zoo when he was a child and thanked the staff who found him.
He made the comments during a state visit to the capital - his first stop on an 11-day tour of Europe and the Middle East.
Watch the US Secretary of State talking about his trip to London as a youngster during a press conference with Foreign Secretary William Hague.
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Mr Kim has made two recent visits to China.
The study looked at the development of 422 children over the course of eight years.
The president said they will come into force if China refuses to change its practices.