You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "who sang the song knocking on heavens door?" whose answer is Bob Dylan.
Each document should contain about 30 words, and these documents should contain useful information.

Query: who sang knocking on heavens door
Useful Output:

Doc 1: Bob Dylan wrote “Knockin' on Heaven's Door” and performed it on its original 1973 release of his soundtrack for the movie Pat Garrett and Billy
Doc 2: Knockin On Heaven's Door is my favorite song G 'NR covers. I have always noticed that only when I hear the song play on the radio, in between each line Axl
Doc 3: Dylan originally wrote the song as part of the soundtrack for the Sam Peckinpah film, Pat Garrett and Billy the Kid.
Doc 4: Guns N' Roses - Knockin' On Heaven's Door (Visualizer) · Comments.
Doc 5: August 1973 marks the release of the single “Knockin' On Heaven's Door”/“Turkey Chase." | August.