難題

それは難題だ。

That's a tall order.

君(きみ)はそれらの難題に対処しなくてはならない。

You have to cope with those difficult problems.

一難去ってまた一難、またまた難題が社長からトップダウンで降りてきたよ。

No sooner had we finished working on one tough problem than the president sent us yet another straight from the top.