**Core Concept**
The active principal of Lathyrus sativa, commonly known as grass pea or chickling pea, is a toxin responsible for neurolathyrism, a motor neuron disease. The toxin acts by inhibiting the synthesis of a crucial amino acid, causing degeneration of motor neurons and leading to muscle weakness and paralysis.

**Why the Correct Answer is Right**
The active principal of Lathyrus sativa is ODAP (oxalyldiaminopropionic acid), also known as BOAA (β-oxalylamino-L-alanine). ODAP inhibits the enzyme 3-phosphoglycerate dehydrogenase, which is essential for the synthesis of serine, a non-essential amino acid. This inhibition leads to a decrease in serine levels, causing a cascade of events that ultimately result in the death of motor neurons.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it is not a known toxin associated with Lathyrus sativa.
**Option B:** This option is incorrect as it is not the correct name of the toxin responsible for neurolathyrism.
**Option C:** This option is incorrect as it is not related to the active principal of Lathyrus sativa.

**Clinical Pearl / High-Yield Fact**
Lathyrism is a classic exam trap, and students should remember that ODAP is the toxin responsible for this condition. The condition is caused by consuming large quantities of Lathyrus sativa, particularly during times of famine or food scarcity.

**Correct Answer:** D. ODAP (oxalyldiaminopropionic acid).