A taxing task or problem is one that requires a lot of mental or physical effort. 费劲的
adjective [原级]费力的;繁重的
It's unlikely that you'll be asked to do anything too taxing. 不大可能叫你去做任何太费劲的事。
verb [vt. 及物动词]征税(tax 的 ing 形式)
Since there is no way for me to avoid exams, I am currently questioning what kind are the most taxing and ultimately beneficial. 既然无法逃避考试,于是我目前在想,哪种考试是最费力但根本上是有益的。