難しい問題(A1): a difficult problem [question]
難しい関係(A2): a difficult relationship
難しい技術(A1): difficult technology
難しい言葉(A1): difficult words
難しい条件(A2): difficult terms
難しい顔(A1): hard look
難しい課題(A2): difficult task [challenge]
難しい現状(B1): challenging current situation, challenging present state of affairs
難しいテーマ(C): a difficult [challenging, thorny] theme
問題が難しい(A1): The problem is difficult.
関係が難しい(A2): have a difficult relationship
対応が難しい(A2): difficult to respond to
対策が難しい(A2): taking measures is difficult
説明が難しい(A2): be hard to explain
勉強が難しい(A1): Studying is difficult.
解決が難しい(A2): It is difficult to find a solution [resolution].
表現が難しい(A2): difficult expressions