Question

complete the sentence.
reflexes and automatic functions such as heart rate and digestion, but it also controls the movement of eyes, arms, and legs.
the brain stem controls not only
not only does the brain stem control

Explanation:

The sentence structure "not only...but also..." requires parallelism. The first option "The brain stem controls not only" would need the "not only" part to be followed by the elements it controls (reflexes and automatic functions). The second option "Not only does the brain stem control" is in the correct inverted structure for "not only" at the beginning of the sentence (when using a verb like "control" in this context, the inversion "does...control" is proper).

Answer:

Not only does the brain stem control