**Core Concept**
Non-depolarizing neuromuscular blockers (NMBs) work by competitively inhibiting the action of acetylcholine (ACh) at the nicotinic receptors on the muscle endplate. This leads to a reduction in the frequency of muscle contractions, eventually resulting in muscle paralysis.

**Why the Correct Answer is Right**
The muscle most resistant to non-depolarizing block is the diaphragm. This is because the diaphragm has a higher concentration of slow-twitch (Type I) muscle fibers, which are less sensitive to NMBs compared to fast-twitch (Type II) muscle fibers. Additionally, the diaphragm has a smaller neuromuscular junction area-to-muscle mass ratio, making it less susceptible to the blocking effects of NMBs.

**Why Each Wrong Option is Incorrect**
* **Option A:** This muscle is actually more susceptible to non-depolarizing block due to its high concentration of fast-twitch fibers.
* **Option B:** Although this muscle is not as resistant as the diaphragm, it is still relatively resistant due to its mixed fiber composition.
* **Option D:** This muscle is highly susceptible to non-depolarizing block due to its high concentration of fast-twitch fibers and large neuromuscular junction area.

**Clinical Pearl / High-Yield Fact**
The order of resistance to non-depolarizing block is: diaphragm > intercostal muscles > abdominal muscles > limb muscles. This knowledge is crucial for managing patients on NMBs, as it helps predict which muscles will be most affected by the blockade.

**Correct Answer: C. Abdominal muscles.**