过去式规则变化
(一) 不变
cut___________ let___________ put_________ read___________ must___________
(二)改成a
come___________ become___________ begin___________
drink___________ have___________
run___________sit___________ring___________sing___________swim ___________give___________
(三)改成ght
think___________fight___________bring___________buy___________catch___________teach___________