YOU SAID:

I can't think of a hard sentence.

INTO JAPANESE

私は難しい文章を考えることができません。

BACK INTO ENGLISH

I can't think of difficult sentences.

INTO JAPANESE

難しい文章は考えられない。

BACK INTO ENGLISH

Difficult sentences are unthinkable.

INTO JAPANESE

難しい文章は考えられない。

BACK INTO ENGLISH

Difficult sentences are unthinkable.