What aspect of this passage is common to much crime/detective fictions?

a) a number of potential suspects are alluded to who will be further developed later on
b) the use of dark imagery paints a sense of imminent danger around the detective
c) it presents an unlikely main character who appears to be clumsy and unqualified

a) a number of potential suspects are alluded to who will be further developed later on

This aspect is common in much crime/detective fiction as it adds suspense and intrigue to the story, allowing the reader to guess and speculate about who the true culprit may be. The development of potential suspects also keeps the reader engaged and eager to discover the truth behind the crime.