unrelenting

他坚持不懈地追求自己的目标，从未放弃。

He showed ___unrelenting determination in pursuing his goals.

教练毫不松懈的要求将团队推向了极限。

The coach's ___unrelenting demands pushed the team to their limits.

连绵不绝的暴雨导致城市部分地区积水严重。

The ___unrelenting rain caused severe flooding in parts of the city.