by引导的倒装句，only

only by引导部分倒转句.

例如：only by working day and night can the couple pay off the debt.只有靠日夜劳作这夫妇从能还清债务。 

这个句子中，情态动词can被移到主语the couple 前，构成部分倒转句。

英语的“only+状语（介词短语/副词/状语从句”位于句首，句子要求用部分倒转，其结构是：only +状语+助动词/情态动词/be动词+主语+谓语+句子的其他成分

例如：

1、Only by working hard can you succeed.

只有努力工作你才能成功。

2、Only in the reading-room can you find him.

你只有在阅览室才能找到他。

英语中only加介词短语放于句首，句子要进行部分倒装。

例如

Only in this way will our school become more and more beautiful.

Only by studying hard will you have the chance to be admitted to your ideal university.

Only by listening to the teacher attentively in class will you make progress.