不定式放句首时,逻辑主语与句子主语要一致：
wrong：To save money,every means has been tried.
right：To save money,he has tried every means.为了省钱,他使出了浑身解数.
wrong：To learn English well,a dictionary is needed.
right：To learn English well,he needs a dictionary.为了学好英语,他需要一本词典.