If blood volume decreased dramatically due to massive bleeding, the autonomic nervous system will attempt to maintain cardiac output by increasing the heart rate.

True. The autonomic nervous system will attempt to maintain cardiac output by increasing the heart rate.

Explanation:

The autonomic nervous system is a system that controls some of the body functions. It acts unconsciously and regulates functions of the body such as the heart rate, respiratory rate, digestion, pupillary response, urination and sexual arousal.

In response to massive bleeding which reduced the volume of blood, stimuli from the baroreceptors( located within the blood vessels and heart) trigger the cardiovascular center of the brain to stimulate sympathetic responses, an action of the autonomic nervous system to increase cardiac output and vasoconstriction. This typically makes the heart rate to increase to approximately 180-200 contractions per minutes and thereby restoring cardiac output to normal level.

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

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explanation: