Answer:
The statement that best explains how Shakespeare transformed the source material is:
While Ensign is highly favored and trusted by the Moor, lago is overlooked by the Moor.
lago being overlooked by the Moor, the Moor transformed Iago into a jealous creature.
Step-by-step explanation:
In Shakespeare’s Othello, Iago's motives are ambiguous and not driven by any lust for Desdemona.
Also in Othello, Shakespeare introduces new characters; they are Roderigo and Desdemona’s father Brabantio.
Cinthio's Gli Hecatommithi is an Italian source for "Othello" and "Measure for Measure" which were written by William Shakespeare.