Answer: A. where no considerable European settlement is possible.
In this excerpt, Chamberlain is discussing the limits and characteristics of the British Empire. In the line "where no considerable European settlement is possible," we can see Chamberlain's true opinions about the other regions of the empire.
The quote implies that European settlements are the "desirable" types of cities, and the height of development. Moreover, he expresses this idea in a way that implies that people living in tropical regions are incapable of sustaining a city of that type. This attitude suggests Chamberlain believes the British to be superior to other countries and cultures around the world.