The answer to your question is Letter C   <-- ANSWER 
Steroid is a molecule made up of four carbon rings with other atoms bonded to those rings. 
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The nervous system and the muscle system respond to stimuli to produce motion. The skeletal movements of muscles are mostly voluntary.
Involuntary movements occur in these muscles when the nerve impulse passes from a sensory neuron to a motor neuron via an interneuron in the spinal cord.
<h3>What are Skeletal muscles?</h3>
Skeletal muscles may be defined as the muscles that fasten to your bones and authorize you to achieve a broad range of activities and operations.
Skeletal muscles control the direct movement of a person's will and are hence referred to as voluntary movement. 
While the spinal cord is associated with both movements directly or indirectly. It is a prolonged, delicate tubelike network liable for holding incoming and outgoing messages through the brain to the rest body.
Therefore, it is well described above. 
To learn more about Skeletal muscles, refer to the link:
brainly.com/question/1283837
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The substances they need are carbon dioxide, water, and chlorophyll, and the substances produced by photosynthesis is 1 glucose molecule and 6 oxygen molecules