The answer is D: "He intended, he said, to devote the rest of his life to learning the remaining twenty-two letters of the alphabet".
This excerpt has been taken from "Animal Farm", written by George Orwell in 1945. "Animal Farm" tells the story of a group of farm animals which rebel against their farmer and start controlling the farm by themselves. According to many, this novel is an allegory of the Russian Revolution and many of the themes presented here reflect our own society. One of these themes is the lack of education which contributes to the vulnerability and oppression of people. Important figures or politicians take advantage of people's ignorance in order to win popularity and have power. One clear example is Boxer, one of the horses in the farm. Although Boxer is a very loyal comrade, he is not very smart and he has been controlled from the very beginning by the selfish pigs. Boxer can not even get past letter 'D' from the alphabet, so, in order to support this idea of lack of education, Orwell includes this passage where Boxer is determined to learn the rest of the remaining letters of the alphabet to be smarter.