**Core Concept**
O.P.C. (Organophosphate Compound) poisoning is a type of cholinesterase inhibition, leading to an accumulation of acetylcholine in the synaptic cleft. This results in overstimulation of muscarinic and nicotinic receptors, causing various systemic symptoms.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of O.P.C. poisoning. The symptoms of O.P.C. poisoning are due to the inhibition of acetylcholinesterase, leading to an increase in acetylcholine levels. This results in overstimulation of muscarinic receptors, causing symptoms such as bradycardia, miosis, and increased salivation. Additionally, the inhibition of acetylcholinesterase can also lead to the accumulation of acetylcholine in the neuromuscular junction, causing muscle weakness and paralysis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a characteristic of O.P.C. poisoning. O.P.C. poisoning primarily affects the muscarinic and nicotinic receptors, causing symptoms such as bradycardia, miosis, and muscle weakness.

**Option B:** This option is incorrect because it is not a characteristic of O.P.C. poisoning. O.P.C. poisoning primarily affects the muscarinic and nicotinic receptors, causing symptoms such as bradycardia, miosis, and muscle weakness.

**Option C:** This option is incorrect because it is a characteristic of O.P.C. poisoning. O.P.C. poisoning can cause muscle weakness and paralysis due to the accumulation of acetylcholine in the neuromuscular junction.

**Clinical Pearl / High-Yield Fact**
A mnemonic to remember the symptoms of O.P.C. poisoning is "SLUDGE", which stands for Salivation, Lacrimation, Urination, Diarrhea, Gastrointestinal upset, and Emesis. This mnemonic can help students remember the various systemic symptoms of O.P.C. poisoning.

**Correct Answer: D.**