C is quite close to being correct but there is one issue.
The passage reads: "for anything that far away [as a quasar] to appear from the Earth the way quasars do, it would have to burn steadily at a rate that produces more light than 90 billion suns would produce."
In comparison, the answer choice reads: "anything that from Earth appears as bright as a quasar does must produce more light than would be produced by 90 billion suns."
These are nearly identical statements; however, the answer choice fails to include "that far away." In failing to include this, the answer choice is saying that anything that appears as bright as a quasar from Earth must produce more light than is produced by 90 billion suns. It is entirely possible that our moon appears as bright as a quasar from Earth but we know that it does not produce more light than 90 billion suns. Therefore, this answer choice is incorrect.
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