Answer: The nervous system
Explanation:
The first part of the embryo to develop is the neural tube, which will become the spinal cord and brain. As the nervous system starts to develop, the tiny heart starts to pump blood, and other parts of the body—such as the digestive tract and backbone—begin to emerge.
Answer:
Target heart rate is generally expressed as a percentage (usually between 50 percent and 85 percent) of your maximum safe heart rate. The maximum rate is based on your age, as subtracted from 220. At an 85 percent level of exertion, your target would be 145 beats per minute.
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