Why is B correct?

Please can I follow up on Shiyi's question here? I also picked A, due to the sentence beginning with "however' in the time theory paragraph! Any top tips for challenging passages such as these?

Rate of speciation, the fourth hypo, tells us that in the tropics evolution happens faster because populations become isolated from each other, while climatic stability points to the fact that extinction happens slower in the tropics because they have more resources.