Step 1: Understand the history of WHO.
The World Health Organization (WHO) was established on 7th April 1948 as the United Nations specialized agency for health, headquartered in Geneva, Switzerland.
Step 2: Analyze the options.
The WHO was established on 7th April, 1948, which corresponds to option (B). The other dates are incorrect.
Step 3: Conclusion.
The WHO was established on 7th April, 1948, making option (B) the correct answer.
Conclusion: The correct answer is (B) 7th April, 1948.