Complex sentence: In this fictional universe, Jonathan and Martha Kent's pickup truck has a flat tire caused by a nail, which prevents them from discovering the spaceship outside Smallville with the baby Kal-El, negating Superman.
Split into simpler sentences: In this fictional universe, Jonathan and Martha Kent's pickup truck has a flat tire caused by a nail. This prevents them from discovering the spaceship outside Smallville with the baby Kal-El, negating Superman.