## Core Concept
The question tests knowledge of historical events in medicine, specifically focusing on the timeline of various medical discoveries and public health initiatives that occurred before 1900 AD. This includes the establishment of social medicine departments, epidemiological studies, nutritional research, vaccine development, and investigations into disease outbreaks.

## Why the Correct Answer is Right
To answer this question correctly, one needs to consider the historical timeline of each event mentioned:
- **Epidemiological work on cholera by John Snow (b)**: John Snow conducted his seminal work on cholera in London in 1854, identifying the source of a cholera outbreak as a contaminated water pump.
- **Work on scurvy by James Lind (c)**: James Lind conducted his experiments on scurvy in 1747, demonstrating the effectiveness of citrus fruits in preventing the disease.
- **Chadwick work on cholera in London (e)**: Edwin Chadwick published his report on "The Sanitary Condition of the Labouring Population" in 1842, which included investigations into cholera outbreaks.

## Why Each Wrong Option is Incorrect
- **Option A: Establishment of seat of social medicine at Oxford (a)**: The establishment of a chair or department of social medicine at Oxford University happened much later than 1900 AD.
- **Option D: Use of BCG vaccine (d)**: The BCG (Bacillus Calmette-Guérin) vaccine was developed in the early 20th century, with the first use in 1921.

## Clinical Pearl / High-Yield Fact
A key point to remember is that John Snow's, James Lind's, and Edwin Chadwick's works were foundational in epidemiology and public health. Specifically, Snow's removal of the contaminated pump handle in 1854 is often cited as one of the earliest examples of epidemiological intervention.

## Correct Answer: B.