If you can't take your heart rate, a good way to recognize that you're exercising efficiently is whether or not
a. it's difficult to have a conversation.
b. you're gasping for breath.
c. your muscles are burning.
d. you're experiencing a little bit of huffing and puffing.

Which description best defines the nervous system and its two main branches? a: the message center of the body, split into the autonomic nervous system and the somatic nervous system b: the control panel of the body, split into the central nervous system and the exterior nervous system c: the message center of the body, split into the central nervous system and the peripheral nervous system d: the control panel of the body, split into the brain and the spinal cord