heavy going
adjective uk/ˌhev.i ˈɡəʊ.ɪŋ/ us/ˌhev.i ˈɡoʊ.ɪŋ/
难读的；难以理解的
difficult to read or understand
I liked the film but the book was rather heavy going. 我喜欢那部电影，但原书读起来却相当费劲。
I'm finding the advanced physics a bit heavy going. 我觉得高等物理有些难懂。