The sympathetic nervous system (SNS) is one of the two divisions of the autonomic nervous system (ANS), which controls involuntary bodily functions. It is responsible for the "fight or flight" response, which prepares the body for action in times of stress or danger. The SNS works by secreting neurotransmitters that stimulate or inhibit various organs and tissues in the body.

The correct answer to the given question is option 'A', which states that the SNS secretes noradrenaline (also known as norepinephrine), which stimulates the organ. Let's explore this in detail:

Noradrenaline as the neurotransmitter:
- Noradrenaline is a neurotransmitter released by the SNS in response to stress or danger.
- It is synthesized in the nerve endings of sympathetic nerves and stored in vesicles.
- When the SNS is activated, noradrenaline is released into the synaptic cleft, the small gap between the nerve endings and the target organ.
- Noradrenaline binds to specific receptors on the target organ, initiating a physiological response.

Stimulation of the organ:
- When noradrenaline binds to receptors on the target organ, it stimulates a response.
- This response can vary depending on the target organ, but generally, it prepares the body for action.
- For example, in the heart, noradrenaline binding to receptors increases heart rate and the force of contraction, increasing blood flow to the muscles.
- In the respiratory system, noradrenaline stimulates bronchodilation, allowing for increased air intake.
- In the liver, noradrenaline promotes the release of glucose into the bloodstream, providing energy for the body's response to stress.

Other options explained:
- Option 'B' (Acetylcholine which stimulates the organ) is incorrect because acetylcholine is the neurotransmitter of the parasympathetic nervous system, not the sympathetic nervous system.
- Option 'C' (Adrenaline which inhibits the organ) is incorrect because adrenaline (also known as epinephrine) is released by the adrenal glands, not the sympathetic nervous system. Adrenaline is involved in the stress response but is not the primary neurotransmitter of the SNS.
- Option 'D' (Acetylcholine which inhibits the organ) is incorrect because acetylcholine is the neurotransmitter of the parasympathetic nervous system, which generally promotes rest, digestion, and relaxation.

In summary, the sympathetic nervous system secretes noradrenaline, which stimulates the target organ and prepares the body for action in times of stress or danger.