Explanation:

- Ellen C. Semple: An American geographer known for her work in environmental determinism, the idea that human activities are shaped by their environment.

- Friedrich Ratzel: A German geographer considered one of the founders of human geography but did not define it as 'the synthetic study of relationship between human societies and earth’s surface.'

- Paul Vidal de la Blache: ? Correct Answer. A French geographer who is credited with defining human geography as ‘the synthetic study of relationship between human societies and earth’s surface.’

- Griffith Taylor: An Australian geographer known for advocating the concept of "possibilism" in geography, emphasizing the role of cultural factors in human-environment relationships.