It was not until he took up fishing that he _____ to relax.
句意: 直到他开始以钓鱼为乐, 他才开始得到了轻松的休息。 此句为强调句, 所强调的时间状语从句部分的动作几乎和主句的动作同时发生, 时间状语从句的谓语动词为过去时, 因而主句的谓语动词采用过去时。