刻苦努力

assiduous / taking great pains

quarter (hour) / moment / to carve / to engrave / to cut / oppressive / classifier for short time intervals

hardworking / assiduous

bitter / hardship / pain / to suffer / to bring suffering to / painstakingly

to exert / to strive

great effort / to strive / to try hard

to make a great effort; to try hard

power / force / strength / ability / strenuously