**Core Concept**
The bacterium *Bacillus anthracis*, the causative agent of anthrax, employs a complex virulence strategy involving multiple factors, including its capsule, toxins, and ability to evade the host's immune response. Understanding these mechanisms is crucial for appreciating the pathogenesis of anthrax.

**Why the Correct Answer is Right**
The anthrax toxin is a tripartite toxin consisting of three main components: lethal factor (LF), edema factor (EF), and protective antigen (PA). However, the toxin is not a complex of two fractions. Instead, it is the product of the interaction between PA and LF or EF. PA acts as a receptor for the toxin and facilitates its entry into the host cell, where LF and EF exert their respective toxic effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Plasmid is responsible for toxin production. This is true, as the plasmid pXO1 in *B. anthracis* carries the genes responsible for toxin production, including those encoding LF, EF, and PA.

**Option B:** Cutaneous anthrax generally resolves spontaneously. This is true, as cutaneous anthrax, the most common form of the disease, typically resolves on its own with supportive care, although it can progress to more severe forms if left untreated.

**Option C:** Capsular polypeptide aids virulence by inhibiting phagocytosis. This is true, as the capsule of *B. anthracis*, composed of a polypeptide called poly-D-glutamic acid, plays a crucial role in evading the host's immune response by inhibiting phagocytosis.

**Clinical Pearl / High-Yield Fact**
The anthrax toxin is highly potent and can cause significant morbidity and mortality if not treated promptly. It is essential to recognize the symptoms of anthrax, including cutaneous lesions, respiratory distress, and gastrointestinal symptoms, and to initiate appropriate treatment, including antibiotics and supportive care.

**✓ Correct Answer: D. Toxin is a complex of two fractions**