**Core Concept**
Carcinoma of the urinary bladder, particularly when confined to the trigone and submucosa, necessitates a management approach that balances local control with the potential for preserving organ function. The choice of treatment hinges on the stage and histological grade of the tumor, as well as the patient's overall health and performance status.

**Why the Correct Answer is Right**
The correct answer, **B. Complete Transurethral resection with intravesical chemotherapy**, is appropriate for this patient due to the localized nature of the tumor. Complete Transurethral Resection of the Bladder Tumor (TURBT) is essential for accurate histological diagnosis and staging, allowing for the assessment of tumor grade and the presence of any high-grade features. Intravesical chemotherapy with a chemotherapeutic agent such as Bacillus Calmette-Guérin (BCG) or Mitomycin C is then administered directly into the bladder to target any residual cancer cells, thereby preventing recurrence and progression. This combination approach offers a balance between local control and the preservation of bladder function.

**Why Each Wrong Option is Incorrect**
**Option A:** Complete Transurethral resection alone is inadequate for managing a tumor with submucosal extension, as it does not address the risk of microscopic disease recurrence.
**Option C:** Palliative Radiotherapy is typically reserved for patients with more advanced disease or those who are not candidates for curative intent therapies, and would not be the primary management strategy for this patient.
**Option D:** Radical Cystectomy, while a definitive treatment for muscle-invasive bladder cancer, is generally reserved for tumors that have invaded the muscularis propria, which is not the case here.

**Clinical Pearl / High-Yield Fact**
Intravesical chemotherapy is most effective when administered within 6-8 weeks of TURBT, as this timing is associated with improved outcomes in terms of recurrence and progression.

**✓ Correct Answer: B. Complete Transurethral resection with intravesical chemotherapy**