Answer:
c. to let the reader know where your evidence comes from 
Step-by-step explanation:
The essay is a type of prose text that analyzes, interprets or evaluates a topic. It is considered a literary genre within the didactic genre. The most representative classic characteristics of an essay are: 
• It is a serious and well-founded writing that synthesizes a significant topic. Which is intended to argue the issue. 
• It has a preliminary, introductory nature, of a preparatory nature. 
• Presents arguments and supported opinions.