It is difficult to convey the sheer complexity of the situation.

很难说清楚形势究竟有多复杂。

The plan's success was balanced on a knife-edge.

计划能否成功还很难说。

It was nip and tuck as to which boat would reach port first.

两船中哪进港都很难说。

It is a tossup whether we shall get there in time.

我们是否能及时赶到那里还很难说。

He's a hard nut to crack.

他是个很难说服的人。

There's no telling what may happen.

很难说会发什么事。

We should get to London before 7 o’clock, but there’s many a slip ’twixt cup and lip.

我们应能在7点钟以前赶到伦敦，可是事情往往很难说准。

But only one reminds me of the courage and persistence it takes to stay the course in the Shadowland.

很难说哪个对我最，而，仅有件能提醒我在阴影之地坚持下去所需的勇气和坚韧不拔精神。

It is hard to say.

很难说。

With so many reports to mislead one, it is hard to say at whose door the responsibility should be laid.

报告多得摸不着头绪, 很难说责任该由谁负。