因为happen的最后一个音节不是重读闭音节词，所以happen现在分词不用双写n: happening
As it happens ， i have left the book at home .偏巧我把书放在家里了。
Such a thing had never happened before .这样的事，过去从未发生过。
What he tells us is unlikely to happen .他告诉我们的，不像是真事。
I shall be interested to know what happens .我很想知道情况会怎样。
Things are happening so fast around here .这里的事情发展得这样快。
He realized at once what was happening .他一眼就看清了当时的情况。
There is no likelihood of that happening .没有发生那种事情的可能。
I can not remember precisely what happened .我记不准所发生的事情了。
We must fulfill the plan ， whatever happens .无论如何要完成计划。
