If the activity level of the sympathetic nervous system increases, the level of activity in the parasympathetic nervous system​

A) ​decreases.
B) ​increases.
C) ​doubles.
D) ​remains constant.

The sympathetic and parasympathetic nervous systems have opposing effects on many bodily functions, including heart rate, respiratory rate, and digestion. When the sympathetic nervous system is activated (e.g. during a "fight or flight" response), heart rate and respiratory rate increase while digestion slows down. In contrast, when the parasympathetic nervous system is activated (e.g. during rest and relaxation), heart rate and respiratory rate decrease while digestion speeds up. Therefore, if the activity level of the sympathetic nervous system increases, the level of activity in the parasympathetic nervous system would have to decrease in order to maintain balance and prevent overstimulation of bodily functions.