Explanation:

- Option 1: Vishnu Sharma

- Vishnu Sharma was an ancient Indian scholar primarily known for "Panchatantra," a collection of animal fables.

- He was not known for writing plays, especially not "Post Office."

- Option 2: Karan Singh

- Karan Singh is an Indian politician and a member of the Indian National Congress.

- He has been involved in cultural and literary initiatives, but he did not write "Post Office."

- Option 3: MK Gandhi

- Mahatma Gandhi was a prominent leader of Indian independence, known for his philosophy of non-violence.

- He was not a playwright and did not author "Post Office."

- Option 4: Rabindranath Tagore

- Rabindranath Tagore was a renowned Bengali poet, writer, and playwright.

- He authored the three-act play, "Post Office," also known as "Dak Ghar."