Refer to the Figure

Refer to the figure. Which statement best describes the role of pathogen associated molecular patterns (PAMPs) in this signal transduction pathway?

A) They are elicitors.
B) They strengthen the cell wall and block plasmodesmata.
C) They are part of a constitutive defense.
D) They attack the pathogen directly.
E) They serve as alarm signals to cells that have not yet been attacked.