it comes about that是什么句型?例如：It came about that he had to cancel his vacation.另外，It came about that he had to cancel his vacation.怎么翻译？

It（形式主语） came about （谓语）that （主语从句的连接词）he had to cancel his vacation（真正主语）.
== It (so) happened that he had to cancel his vacation
cancel ==call off, give up , stop ----取消

句子翻译：他取消了他的假期。

it作形式主语，真正的主语由后面的that从句充当。
意思为，结果他不得不取消他的假期。

指发生了什么事
It（形式主语） came about （谓语）that he had to cancel his vacation（主语从句）.
结果他取消了他的假期
come about 发生（不及物）