【答案解析】occur：发生。happen：发生。又如：His death occurred the following year．他次年就死了。 I can remember the whole thing as if it happened yesterday．我记得整个事情如同发生在昨天一样。break：碎；断。break out：突然发生。The economic crisis broke out first in the US，经济危机首先在美国发生。appear：出现。A smile gradually appeared on her face．微笑逐渐浮现在她的脸上。