Explanation:

- Option 1: Bandhua Mukti Morcha Vs. Union of India 1983, Supreme Court

- This case stated that even a letter addressed to the Supreme Court can be treated as a writ petition. It pioneered the concept of Public Interest Litigation (PIL) in India.

- Option 2: Sheela Barse Vs. State of Maharashtra 1983, Supreme Court

- Focused on the inhumane conditions of women prisoners, highlighting their rights.

- Option 3: SP Gupta Vs. Union of India, 1981, Supreme Court

- Known as the "Judges Transfer case," it dealt with judicial independence and transparency.

- Option 4: Hussainara Khatoon Vs. Home Secretary, State of Bihar

- Highlighted the right to a speedy trial as part of the fundamental rights under the Indian Constitution.