Explanation
Correct answer: C.
Choice C is the best answer. “Thus” logically signals that the action described in this sentence—the researcher being able to determine the chemical makeup of the planet’s bright regions based on how they reflect light—is a result or consequence of the previous information about spectroscopic fingerprints.
Why the other choices are wrong
Choice A
Choice A is incorrect because “regardless” illogically signals that the action described in this sentence occurs despite the previous information about spectroscopic fingerprints. Instead, the finding in this sentence is a result or consequence of that information.
Choice B
Choice B is incorrect because “meanwhile” illogically signals that the action described in this sentence either occurs at the same time as or offers an alternative to the previous information about spectroscopic fingerprints. Instead, the finding in this sentence is a result or consequence of that information.
Choice D
Choice D is incorrect because “in comparison” illogically signals that the action described in this sentence is being compared with the previous information about spectroscopic fingerprints. Instead, the finding in this sentence is a result or consequence of that information.