24. Just as plant species native to regions with browsing mammals evolved many natural anti-browser defenses (such as sharp spines and toxic chemicals), so humans in malarial regions have evolved dozens of chemical defenses against malaria.
(A) so humans in malarial regions have evolved dozens of chemical defenses against malaria
(B) humans in malarial regions have been evolving dozens of chemical defenses against malaria
(C) there has been, in malarial regions, an evolution of dozens of human chemical defenses against malaria
(D) dozens of chemical defenses against malaria have been evolved by humans in malarial regions（A）
(E) similarly, in malarial regions, humans have evolved dozens of chemical defenses against malaria
I choose B, but the answer is A.
1) A is right because of the verb form "have evolved"?
2) Why there is "so" in A? Looks weird. Is it a right idom "Just as... so..."? | 
