詩 and 韻文: a poem and the form of verse
Read 詩 as a poem that is written or introduced, and 韻文 as the form of a prologue or the result of rewriting prose.
詩: writing a short poem and introducing one poem
「窓辺で雨の音を聞きながら短い詩を書いた。」 means “I wrote a short poem while listening to the rain by the window.” 詩（し） means a poem or poetry. ながら links writing the poem with listening to the rain, while 窓辺で gives the setting by the window.
「朗読会で好きな詩を一編紹介した。」 means “I introduced one of my favorite poems at the reading.” 好きな詩を一編 identifies one favorite poem. 紹介した describes introducing that work; it does not identify the person introducing it as its author.
韻文: a prologue’s form and the result of rewriting
「古い物語の序章は韻文で書かれている。」 means “The prologue of the old story is written in verse.” 韻文（いんぶん） means verse. The part described as written in verse is the old story’s 序章, its prologue, rather than an assertion about every part of the story.
「授業で散文を短い韻文に書き換えた。」 means “In class, we rewrote prose as a short verse.” 散文を短い韻文に書き換えた describes rewriting prose as short verse. に marks the resulting form; 書き換えた is rewriting, not simply selecting an unchanged excerpt.
A work to introduce and a form to write in
詩を一編紹介した focuses on the single work that was introduced. 韻文で書かれている focuses on the form in which a text is written, so the two expressions answer different questions in these examples.
散文 is the text before the change, and 短い韻文 is the resulting form. Following 書き換えた keeps this transformation distinct from deletion or excerpting, and from introducing a poem at a reading.
Does 授業で散文を短い韻文に書き換えた mean that an unchanged passage was excerpted from the prose?
Show the answer and why
No. In class, we rewrote prose as short verse. 書き換えた names the rewriting action, and 韻文 names its resulting form; this differs from introducing a poem in 詩を一編紹介した.