The two options that best support Sadie's research regarding the shift from fish fossils to cactus fossils in the sedimentary rock layer are:
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Due to the Law of Superposition, the fossils in the bottom layer are older.
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The environment conditions have changed over time.
These choices indicate that the bottom layer's fossils are from an earlier time, specifically when the environment was suitable for fish, while the upper layers reflect a more recent environment, which is now more suitable for cacti.