这份工作需要长时间集中注意力，真是太费神了。

This job requires intense focus for long hours, it's really ___hard.

这块木头非常坚硬，很难用普通的工具切割。

This piece of wood is very ___hard and difficult to cut with ordinary tools.

这个数学题对我来说太难了。

This math problem is too ___hard for me.

他使劲地敲了敲门，但没人回应。

He knocked on the door ___hard, but no one answered.

她努力学习，终于在考试中取得了好成绩。

She studied ___hard and finally got good grades in the exam.