The answer is B: to propose the theory of evolution.
Explanation:
Charles Darwin was an English naturalist who published his work on the evolution in his book "On the origin of species". Darwin talked about the natural selection, i.e. the selection done by nature. He studied the flora and fauna of Galapagos Islands. He found that there were many varieties of small black birds in these islands which differed mainly in the shape of beaks and feeding habits. These were later called darwin finches.
