Clause A,于是乎 + Clause B
于是乎 is a more literary or emphatic variant of 于是, meaning "and so" or "thereupon." It functions the same way, connecting a cause to its consequence, but carries a slightly formal or dramatic tone. It is more common in written Chinese and storytelling.
他想了半天也没有办法,于是乎只好求助朋友。
Tā xiǎng le bàntiān yě méiyǒu bànfǎ, yúshìhū zhǐhǎo qiúzhù péngyǒu.
He thought for a long time but couldn't find a solution, so he had no choice but to ask a friend for help.
消息传开了,于是乎大家纷纷赶来帮忙。
Xiāoxi chuán kāi le, yúshìhū dàjiā fēnfēn gǎn lái bāngmáng.
The news spread, and so everyone rushed over to help.
钱花光了,于是乎他开始认真找工作。
Qián huāguāng le, yúshìhū tā kāishǐ rènzhēn zhǎo gōngzuò.
The money was all spent, so he started seriously looking for a job.