I am new here and this is the first thing i'm doing on this site but to answer the question, i believe the excerpt is written from a first person point of view.
The sentence that uses the past participle form of the verb write is the second sentence: Ali wrote his book report last night.
Cave is a smaller section of a cavern. A song is a smaller part of a tune. Therefore, one is the bigger picture (second section) and the other is the smaller picture (first one) Hope this helps!