Answer:
A Muscle Contraction Is Triggered When an Action Potential Travels Along the Nerves to the Muscles. Muscle contraction begins when the nervous system generates a signal. The signal, an impulse called an action potential, travels through a type of nerve cell called a motor neuron.
A fragment sentence is usually something doesn't really finishes properly, it doesn't stand out so it would be a pencil, four sheets of paper, and a ruler.
The earth moving and shifting the ground below.
4. Petroleum.
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