It is hard to believe.

这很难相信。

It is hard to lift stones this size.

把这么大的石头举起来很费力。

It is hard to be healthy without wealth.

没有财富很难健康。

It is hard to quantify happiness.

很难量化幸福感。

It is hard to breathe on smoggy days.

在烟雾弥漫的日子里很难呼吸。

It is hard to see the road sign at night.

夜晚开车时，路标很难看清。

Sometimes it is hard to forgive and forget.

有时候原谅和忘记是很难的。

It is hard to wake up early in the morning.

早上早起很困难。

It is hard to distinguish directions in the dark.

在黑暗中很难分辨方向。

Her smile has implied meaning; it is hard to decipher.

她的微笑有寓意，让人捉摸不透。