Final answer:
The main plot elements of Dr. Manhattan's exile on Mars and Ozymandias's plan from the 'Watchmen' graphic novel were kept unchanged in Zack Snyder's film adaptation, making the statement true.
Step-by-step explanation:
The statement that Zack Snyder kept the main thrust of the plot unchanged in his adaptation of "Watchmen" is True. Dr. Manhattan's self-imposed exile on Mars and Adrian Veidt, also known as Ozymandias's plan to unite the world by orchestrating a nuclear attack, are critical plot points in both the graphic novel and the movie. While some creative liberties were indeed taken, these central elements of the storyline remain consistent with the source material.