problematic

翻译：对中国学生来说，英语中的双元音（diphthong）很难掌握。

For the Chinese students that the diphthong of the English is problematic .

参考翻译：English diphthongs are particularly problematic for Chinese students to master

造句：西游记中师徒四人西天取经真是困难重重。

In the Journey to the west learn from the west has been problematic for the four mentoring.

形容词：困难重重