What year was the Declaration of Helsinki released?

The Declaration of Helsinki was released in 1964, making option C the correct choice. Option A, 1947, is not correct because that is when the Nuremberg Code was released, not the Declaration of Helsinki. Option B, 1954, is also incorrect because that is when the World Medical Association was founded, not when the Declaration of Helsinki was released. Option D, 1971, is incorrect because that is when the Tokyo Declaration was released, not the Declaration of Helsinki. Therefore, option C is the only correct option.