Answer:
The need for continental time zones stemmed directly from the problems of moving passengers and freight over the thousands of miles of rail line that covered North America by the 1880s. Since human beings had first begun keeping track of time, they set their clocks to the local movement of the sun.
When you shiver, that's actually how you help yourself stay warm! It's your immediate instinct reaction to do so when you're cold, so there will be more heat produced, and they occur by your muscles moving. =)
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