Which contribution to the body of scientific knowledge is most recent?

B)the confirmation of the double-helix structure of DNA

Research method is always used to answer every scientific inquiry and in gaining evidential data or knowledge. The scientific method has the following process or at least undergoes the process of
1. Observation 
2. Hypothesis 
3. Experimentation 
4. Interpretation of data 
5. Evaluating the data 
6. Passing and recording the data

He used pea plants to study the patterns of heredity.