The correct option is D Frederick Blackman
Frederick Blackman proposed the law of limiting factors in 1905.
This law states that " If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: it is the factor which directly affects the process if its quantity is changed".
Robert Hill demonstrated the 'Hill reaction' of photosynthesis, proving that oxygen is evolved during the light requiring steps of photosynthesis.
Melvin Calvin and Hans Adolf Krebs are best known for discovering the Calvin cycle and the Citric acid cycle, respectively.