After years of contemplation, they finally took the plunge and started their own business.

took 是动词 take 的过去式，take 的基本意思是"拿、取"，在不同短语中有不同含义。 the 是定冠词，用于特指某个事物或情况。 plunge 是名词，意思是"突然投入、猛冲"，常用来形容突然采取行动或冒险。 took the plunge 是一个固定短语，字面意思是"跳入水中"，比喻"下定决心做某事"，尤其指经过深思熟虑后终于采取行动。