**Core Concept**
The question is testing knowledge of the history and development of neuromuscular blocking agents, which are crucial in anesthesia for facilitating tracheal intubation and providing muscle relaxation during surgery. **Neuromuscular blockers** act by interfering with transmission at the neuromuscular junction, either by competing with acetylcholine for receptor sites or by destroying the receptor.

**Why the Correct Answer is Right**
The first neuromuscular blocker was indeed **d-Tubocurarine**, a non-depolarizing agent that competes with acetylcholine for nicotinic receptors at the neuromuscular junction, thereby preventing muscle contraction. Its discovery and introduction into clinical practice marked the beginning of a new era in anesthesia and surgery.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not specified and thus cannot be evaluated.
**Option B:** Incorrect as it is not provided, thus lacking the necessary information to be considered.
**Option C:** Incorrect because, similar to options A and B, it lacks specification.
**Option D:** Also incorrect due to the absence of a specified answer choice.

**Clinical Pearl / High-Yield Fact**
Remembering **d-Tubocurarine** as the first neuromuscular blocker is crucial for understanding the historical development of anesthesia practices. This knowledge can help in comprehending the mechanism and application of subsequent neuromuscular blockers.

**Correct Answer:** D. d-Tubocurarine.