## Core Concept
The question pertains to the characteristics and usage of an oesophagoscope, a medical instrument used for visually examining the esophagus. This involves understanding the types of oesophagoscopes, their applications, and safety considerations.

## Why the Correct Answer is Right
Flexible oesophagoscopy is a commonly used procedure for diagnosing and sometimes treating conditions affecting the esophagus. It involves the insertion of a flexible tube with a camera and light on the end, allowing for direct visualization of the esophageal mucosa. This method is preferred for its safety and efficacy in outpatient settings.

## Why Each Wrong Option is Incorrect
- **Option A:** While rigid oesophagoscopy does exist and is used for certain procedures, especially therapeutic ones, the statement about its use might not align with current practices favoring flexible oesophagoscopy for diagnostic purposes.
- **Option B:** This option might discuss a specific aspect of oesophagoscopy that is not universally accurate or relevant.
- **Option C:** Similarly, this could pertain to a detail that does not broadly apply or is not accurate in the context of oesophagoscopy.
- **Option D:** Without specific details on what each option states, it's implied that the incorrect options provide information that is not accurate or relevant regarding oesophagoscopy.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **flexible oesophagoscopy** is widely used for diagnosing esophageal diseases due to its safety profile, allowing for examination under conscious sedation. It's crucial to note that **oesophagoscopy** can be both diagnostic and therapeutic, especially with the advancement in endoscopic techniques.

## Correct Answer: D.