苦功[kǔ gōng]
词典hard work：繁重的工作；劳苦；苦工；苦功。
词典painstaking effort：苦功；心血。
hard work; painstaking effort:
例：下苦功
take pains; make painstaking efforts;
下苦功学习
study hard;
她下苦功学习英语， 获得了高分。
She took great pains with her English lessons and got high marks.