Why do the the authors of lobs girl and jeremiah’s song use flashbacks

They use flashbacks "to inform all the more concerning a character".  

Flashback is an intrusion of the sequential succession (starting at a film or artistic work) of an occasion of prior event. Flashbacks are intrusions that essayists do to embed past occasions, with a specific end goal to give foundation or setting to the present occasions of an account.

concern the charecter

Explanation:

about the letter or who wrote the letter

the answer is b:   the american composer and singer bob dylan composed many songs, by which he is very famous and considered one of the mosts influencial artists of pop music. he was awarded the nobel prize in literature for his type of poetry. but the huge impact his songs had are due to both lyrics and music, without which the message would lose strength.