Other mistake: After realising they can track the mother box, Batman says they have to go back to his base to use one of his satellites to track it, and they all do so. Which completely ignores the fact that Cyborg could easily access the satellite feed directly using his abilities and display it to the others on any nearby screen in Star Labs.
Zack Snyder's Justice League (2021)
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Directed by: Zack Snyder
Starring: Ben Affleck, Amy Adams, Jared Leto, Henry Cavill, Gal Gadot, Ezra Miller, Ray Fisher
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Suggested correction: Just because he had many options available to him, does not mean that the option which he chose was wrong.
Wonder Woman: You said the age of heroes would never come again.
Bruce Wayne: It will. It has to.
Trivia: The truck that crashes in Central City has the name Gard'Ner Fox on it. Gardner Fox was a writer for DC comics and also created The Flash, Hawkman and the Justice League.
Question: When did Martian Manhunter get to Earth, why did he assume Martha Kent's identity, and where is she during Justice League?
Answer: Martian Manhunter is played by Harry Lennix, who also plays General Swanwick, a character who appears in Man of Steel and Batman v Superman (and we can see he transforms back into Swanwick he leaves), revealing that Swanwick was Martian Manhunter the whole time, so the indication is he got to Earth before Man of Steel. He assumed Martha's identity to speak with Lois, specifically to have a heart to heart with her as she is depressed due to Clark's death. Martha is present every other time we see her, when she leaves the Kent home at the beginning and when she reunites with Clark later on. This scene was the only time Martian Manhunter used her identity.