Step 1: Understand the principle.
The idea is that a person is presumed innocent until proved guilty by a fair trial.
Step 2: Recall the UDHR.
The Universal Declaration of Human Rights was adopted on 10 December 1948 and lists global human rights standards.
Step 3: Place the principle.
Article 11(1) of the UDHR states the presumption of innocence and the right to a fair trial with defence guarantees.
Step 4: Rule out the others.
Article 9 covers arbitrary arrest, Article 20 freedom of assembly, and Article 21 participation in government.
Answer: Article 11 (Option 3).