It was cause by an improbable concatenation of circumstances .
这是由奇异的事件的连接造成的.
The arab revolt of 2011 belongs to a rare class of historical events : a concatenation of political upheavals , one detonating the other , across an entire region of the world .
A warm , sunny day at a particular time and place , as desirable as it may be to human beings , is not a good as long as we are unable to control the natural forces whose concatenation produces it .
