personally think 'a' is the best answer
It’s called an onomatopoeia, they are used a lot in comic books. :)
Answer:
The Great Gatsby
I was immediately struck by the number of young Englishmen dotted about; all well dressed, all looking a little hungry and all talking in low earnest voices to solid and prosperous Americans. I was sure that they were selling something: bonds or insurance or automobiles. They were at least agonizingly aware of the easy money in the vicinity and convinced that it was theirs for a few words in the right key.