Lipids are made up of carbon, hydrogen, and oxygen. So I'm assuming A would be the best answer. Proteins are made up of carbon, hydrogen, oxygen, and nitrogen and nucleic acids are made up of carbon, hydrogen, oxygen, nitrogen, and phosphorus.
When a stimulus is produced it signifies the production of sensation in the sensory organs. This sensation through the sensory organs (eyes, ears, nose, skin and tongue) is sent to the sensory nerve connected to these sense organs. These sensory nerves send nerve impulses through the nerve fiber to the spinal cord. From the spinal cord the nerve impulse is transferred to motor nerves.
The motor nerve then sends response to the stimulus though the same path to the region from which stimulus was received and thus the body responds through muscular activity. Such as removal of heat from the heated object if heated sensations were received.
Natural system is former when various components get grouped together for a particular function
