LONDON (Reuters) - China holds the key to resolving the North Korean nuclear crisis and must do more to use all its influence and levers to deal with its neighbor, British Defence Secretary Michael Fallon said on Wednesday.  China holds the key, the oil to North Korea flows from China ... China has not just influence but has many of the levers that are needed to change behavior in North Korea,  Fallon told BBC radio.  (U.S. Defence) Secretary (Jim) Mattis and I and others across the administration are very clear that we have to absolutely exhaust every possible diplomatic avenue to get this situation under control now, that means working intensively in New York over the next few days to get a new (UN) resolution, it means looking at the existing sanctions and making sure they are properly enforced...  Above all it means putting more pressure on China to deal with its neighbor.   