Answer: A. it is unclear whether or not warming of the planet is occurring
Explanation:
The thalamus is a bundle of about twelve nuclei in which every sense except smell has a synapse; it is the "gateway" to the cerebral cortex. The correct answer to blank above is "is a bundle of about twelve nuclei in which every sense except smell has a synapse; it is the "gateway" to the cerebral cortex".
This is what we call a theory in science in its strictest sense. When we're talking about theories in science we're talking about culminations of datasets that have up to this point always been true, however, we're leaving the posibility that they will once be wrong still open.